Ch. 5 Flashcards
Sediment
Any solid fragment of inorganic or organic material
• Rocks and cobble at the beach
• Fragments of seashells
• Sand and mud at the bottom of the bay
Principle of Superposition
In a deposit of undisturbed sedimentary rock layers, the oldest rocks are at the base of the deposit and the youngest rocks are at the top
Paleoceanography
The study of the Earth’s history in the ocean’s sedimentary record.
Sediment cores
Long, narrow-diameter cylinders of sediments, some of which may be hundreds of feet long.
Challenger Expedition
The first oceanographic expedition to study the global distribution of sediments in the world ocean
Foraminifera
Microscopic marine organisms found throughout the world ocean
Wolfgang Schott
Determined that the absence of foraminifera skeletons in the lower layers of the core was caused by cold seawater temperatures
Cesare Emiliani
Determined that the ratio of Oxygen18/Oxygen16 changed based on water temperature.
Colder waters had a higher concentration of Oxygen18 (+3.5%)
Warmer waters had a lower concentration of Oxygen18 (0 to -2%)
Kullenberg piston corer
An instrument that enabled oceanographers to obtain 10-20 m sediment cores representing 1-2 million years of deposition
CLIMAP
Climate: Long-Range Investigation, Mapping, and Prediction
Milankovitch cycle
Millennial-scale deviations in Earth’s orbit around the Sun that causes ice ages
Heinrich events
Abrupt climate change in the form of rapid cooling within decades to centuries
Oxygen18
A stable isotope of Oxygen in the shells of foraminifera
Name some sources of marine sediments
Continental and oceanic crust Volcanoes Microbes Plants and animals Chemical processes Outer space
Why is it difficult to identify the source of sediment?
It may have been altered form its original form by physical, chemical, or biological processes
Descriptive classification
Visual analysis of the texture and composition of a sediment sample
Size classification
Based on visual, mechanical, or laser-based sizing of sediments, aids in understanding physical and chemical changes in sediments that occur during transport and deposition
Genetic classification
A more complete description of the physical, chemical, and biological properties of sediments
Logging
A visual classification system where an oceanographer creates a written description of sediments obtained while at sea. This will be used as a guide for more detailed analysis at shore.
Two broad categories of sediments
Granular
Chemical
Granular
Results from the fragmentation of inorganic or organic parent materials (e.g., mud, silt, sand, and microscopic shells of marine organisms). They can be formed by mechanical, biological, or volcanic processes.
Chemical
Forming directly from dissolved compounds in seawater
Mechanical Processes
Weathering and erosion
Biological processes
Secretion of cell or mineralized cell wall
Volcanic processes
Above- of below-water ejection of ash and particles
Categories of granular sediments
Biogenous
Lithogenous
Biogenous
Originating from biological processes, i.e., from organisms that secrete mineral skeletons. They are subdivided into calcareous and siliceous.
Lithogenous
Originating from rocks
Chemical sediment categories
Hydrogenous
Authidgenic
Hydrogenous
Coming from water
Authigenic
Forming in place
Examples of chemical sediments
- Limestone and limestone-like rocks resulting from the mineralized remains of marine organisms whose cell walls are made of calcium carbonate
- Evaporites
- Metalliferous compounds produced by hydrothermal vents
- Manganese nodules
Diatoms
Single-celled, photosynthetic microbes whose cell walls are constructed of silica
How are biogenous sediment named?
For the type of organism that formed the sediment
Tektites
A special class of lithogenous sediments that have undergone what is known as shock metamorphism. They originate from the ejection of melted fragments of terrestrial rocks during meteorite impacts.
Interplanetary dust particles
Cosmic dust. They are enriched in He3, an isotope of Helium
Cosmogenous sediment
Small particles, captured by Earth’s gravitational field, that originate from asteroids, active comets, and other planetary objects in the solar system.
Udden-Wentworth scale
The classification of sediments by their diameter
Sedimentation
Sedimentary processes; the processes that involve the production, transport, and deposition of sediments
How are sediments produced?
Through the erosion of rocks, mostly continental, and through the activities of organisms, especially microorganisms that form skeletons or shells
How does the transport of sediments occur?
By winds, rivers, ocean currents, ice flows, glaciers, and a number of other geological processes
Sediment Cycle
- Origination
- Transport
- Deposition
- Destruction
Hydrologic cycle
The solar- and gravity-driven exchange of water between various reservoirs
Continental weathering
The dissolution, fracturing, or chemical alteration of rocks through physical, chemical, or biological processes
Physical/mechanical weathering
The breaking apart or fragmentation of rocks due to rock slides, debris flows, and other processes, such as earthquakes
Chemical weathering
Arises due to oxidation of minerals or elements within minerals, dissolution by natural acids, and dissolution of rocks in water
Biological weathering
Stems from the activities of organisms that fracture, dissolve, or chemically alter rocks
In what ways does weathering vary?
According to the following: Chemical makeup of the rock Climate Presence of soil Length of exposure of the rock at the surface
Threshold velocity
The speed of fluid flow (Air or water) that causes a particular sediment to move
Three types of sediment movement
- Rolling
- Saltation
- Suspension
Rolling movement
The tumbling of a grain along a surface
Saltation movement
The hopping of a grain along a surface
Suspension movement
The floating of a grain within the fluid
Grain size distribution
The proportions of different sizes of grains within sediment
Well-sorted
A sample of sediment where the grains exhibit a narrow range of sizes
Poorly sorted
A sample of sediment where the grains exhibit a wide range of sizes
Why does sorting occur?
Grains of different sizes and densities behave differently under a given flow
Stoke’s Law
The method of rating the sinking of fine particles mathematically
Sediment trap
An instrument that allows for the direct measurement of particle sinking rates
