Glossary

Coal

Fact Sheet:

Chemical Composition: Primarily carbon, with varying amounts of hydrogen, sulfur, oxygen, and nitrogen
Hardness: 1 to 2 on the Mohs scale (varies by coal type)
Formation: Sedimentary rock formed from the accumulation and decomposition of organic matter, primarily plant material
Color Varieties: Black, brownish-black
Major Localities: United States, China, India, Australia, Russia, and South Africa
Common Uses: Electricity generation, steel production, cement manufacturing, and as a liquid fuel

Introduction: Coal is one of the world’s most important energy resources, playing a pivotal role in the development of modern industrial societies. Formed over millions of years ...

^DDeformation

Deformation refers to the alteration of the shape or volume of a rock body in response to stress, including processes like folding, faulting, and fracturing. Deformation is a key concept in structural geology and tectonics, helping to explain the formation of mountains, earthquakes, and other geological structures.

Reference: Twiss, R. J., & Moores, E. M. (2007). “Structural Geology.” W. H. Freeman.

^DDeformation Bands

Deformation bands are narrow zones of localized strain in porous rocks, often associated with faulting and folding. These bands can form due to mechanical compaction, cataclasis, or grain reorganization and can significantly influence the permeability and mechanical properties of the rock. Deformation bands are important in the study of structural geology, fault mechanics, and reservoir characterization.

Reference: Aydin, A., & Johnson, A. M. (1983). “Analysis of Faults and Deformation Bands in Sandstone.” Journal of Structural Geology, 5(1), 19-31.

^DDelta

A delta is a landform formed at the mouth of a river, where it deposits sediment as it flows into a slower-moving or standing body of water, such as an ocean, sea, or lake. Deltas are characterized by their branching network of distributaries and are classified based on the dominant processes that shape them: river-dominated, wave-dominated, or tide-dominated. Deltas are significant in sedimentology, coastal geomorphology, and are often fertile areas for agriculture.

Reference: Coleman, J. M., & Wright, L. D. (1975). “Deltas: Processes of Deposition and Models for Exploration.” Continuing Education Publishing Co.

^DDendritic Drainage Pattern

A dendritic drainage pattern resembles the branches of a tree, with many small tributaries joining together to form larger streams and rivers. This pattern develops in regions of relatively uniform rock or soil, where the underlying material does not strongly influence the direction of stream flow. Dendritic patterns are significant in geomorphology for interpreting the characteristics of the underlying substrate and landscape evolution.

Reference: Howard, A. D. (1994). “A Detachment-Limited Model of Drainage Basin Evolution.” Water Resources Research, 30(7), 2261-2285.

^DDeposition

Deposition is the geological process by which sediments, soil, and rocks are added to a landform or landmass. This occurs when the forces transporting the particles, such as water, wind, or ice, lose energy and drop the material. Deposition is fundamental in the formation of sedimentary rocks, the creation of landforms like deltas and beaches, and the development of stratigraphic layers.

Reference: Boggs, S. (2011). “Principles of Sedimentology and Stratigraphy.” Pearson.

^DDesert Pavement

Desert pavement is a natural surface covering of closely packed, interlocking angular or rounded rock fragments found in arid regions. It forms through the gradual removal of fine particles by wind and water, leaving behind a layer of coarser material. Desert pavements play a critical role in protecting underlying soils from erosion and are important indicators of long-term climatic stability in deserts.

Reference: McFadden, L. D., Wells, S. G., & Dohrenwend, J. C. (1987). “Influences of Quaternary Climatic Changes on Processes of Soil Development on Desert Loess Deposits of the Cima Volcanic Field, California.” Catena, 14(4), 361-389.

^DDesert Varnish

Desert varnish is a dark, glossy coating found on the surface of rocks in arid environments, composed of clay minerals, oxides of manganese and iron, and organic material. It forms over long periods of time through the action of wind and water, and its study can provide insights into past environmental conditions and the history of the landscape.

Reference: Dorn, R. I. (1998). “Rock Coatings.” Elsevier.

^DDesertification

Desertification is the process by which fertile land becomes desert, typically as a result of drought, deforestation, or inappropriate agricultural practices. It leads to the loss of productive land and biodiversity and is a major environmental issue in arid and semi-arid regions. Desertification is significant in environmental science, land management, and global sustainability efforts.

Reference: UNCCD (1994). “United Nations Convention to Combat Desertification.” United Nations.

^DDetachment Fault

A detachment fault is a low-angle normal fault that typically separates highly deformed rocks in its hanging wall from less deformed rocks in its footwall. These faults are often associated with large-scale extensional tectonics and can be linked to the formation of metamorphic core complexes. Detachment faults are significant in understanding the tectonic evolution of extensional terrains.

Reference: Wernicke, B. (1981). “Low-Angle Normal Faults in the Basin and Range Province: Nappe Tectonics in an Extending Orogen.” Nature, 291(5810), 645-648.

^DDetritus

Detritus refers to loose fragments of rock and mineral material that have been broken down by weathering and erosion. These fragments can range in size from boulders to clay particles and are typically transported by wind, water, or ice before being deposited as sediment. Detritus is a key component of sedimentary processes and plays a crucial role in the formation of sedimentary rocks.

Reference: Pettijohn, F. J., Potter, P. E., & Siever, R. (1987). “Sand and Sandstone.” Springer.

^DDiatomite

Diatomite is a soft, siliceous sedimentary rock composed mainly of the fossilized remains of diatoms, a type of microscopic algae. It is highly porous and has a wide range of industrial applications, including filtration, insulation, and as a lightweight aggregate. Diatomite is important in paleoenvironmental studies, as it provides a record of past climatic and ecological conditions.

Reference: Round, F. E., Crawford, R. M., & Mann, D. G. (1990). “The Diatoms: Biology and Morphology of the Genera.” Cambridge University Press.

^DDiatreme

A diatreme is a volcanic pipe or vent formed by a gas-charged explosive eruption that blasts through the Earth’s crust, creating a steep-sided, often funnel-shaped, breccia-filled conduit. Diatremes are commonly associated with kimberlite pipes, which can contain diamonds. They are significant in the study of volcanology and economic geology, particularly in diamond exploration.

Reference: Kjarsgaard, B. A., & Levinson, A. A. (2002). “Diamonds in Canada.” Geoscience Canada, 29(2), 71-84.

^DDifferential Erosion

Differential erosion occurs when different types of rocks or sediments erode at different rates due to variations in hardness, composition, or structure. This process can lead to the formation of distinct landforms, such as mesas, buttes, and valleys. Differential erosion is significant in the study of geomorphology and landscape evolution.

Reference: Twidale, C. R. (1982). “Granite Landforms.” Elsevier.

^DDike (Geology)

A dike is a sheet-like intrusion of igneous rock that cuts through pre-existing rock layers, typically formed when magma intrudes into cracks and solidifies. Dikes can vary in width and length, and they often form in regions of tectonic activity. They are important for understanding the plumbing systems of volcanoes, the direction of past tectonic stresses, and the emplacement of magma within the Earth’s crust.

Reference: Pollard, D. D., & Johnson, A. M. (1973). “Mechanics of Growth of Some Laccolithic Intrusions in the Henry Mountains, Utah, II: Bending and Failure of Overburden Layers and Sill Formation.” Tectonophysics, 18(3-4), 311-354.

^DDiluvial

The term “diluvial” refers to geological processes or deposits associated with the action of large-scale floods or the runoff from melting glaciers, particularly those related to past glacial periods. Diluvial deposits can include large-scale gravel and sand beds, indicating ancient flood events. Understanding diluvial processes is important in reconstructing past climate events and landscape changes.

Reference: Baker, V. R. (1978). “The Spokane Flood Controversy and the Martian Outflow Channels.” Science, 202(4374), 1249-1256.

^DDrag Fold

A drag fold is a small-scale fold that forms adjacent to a fault, where the movement along the fault causes the rock layers to bend. Drag folds are typically asymmetrical and provide valuable insights into the direction and sense of fault movement. They are important structures in structural geology for interpreting the kinematics of fault zones.

Reference: Ramsay, J. G., & Huber, M. I. (1987). “The Techniques of Modern Structural Geology, Volume 2: Folds and Fractures.” Academic Press.

^DDrainage Basin

A drainage basin, also known as a watershed or catchment area, is the geographic area that contributes water to a particular stream, river, or lake. It is defined by topographic divides, where all precipitation within the basin eventually drains into a common outlet. Drainage basins are critical in hydrology, water resource management, and environmental studies, as they influence water flow, sediment transport, and ecosystem health.

Reference: Chorley, R. J., Schumm, S. A., & Sugden, D. E. (1984). “Geomorphology.” Methuen.

^DDrainage Divide

A drainage divide is a geographical boundary separating neighboring drainage basins, where precipitation on either side of the divide flows into different bodies of water. Drainage divides can range from sharp ridges, such as mountain crests, to subtle topographic boundaries. They are crucial in hydrology, determining the direction of water flow and influencing river systems.

Reference: Twidale, C. R. (2004). “River Patterns and Their Meaning.” Earth-Science Reviews, 67(3-4), 159-218.

^DDrift (Glacial)

Glacial drift refers to all the materials, including boulders, sand, clay, and silt, deposited directly or indirectly by glaciers. It includes both till, which is deposited directly by the ice, and outwash, which is deposited by meltwater. Glacial drift is important for understanding past glacial movements, the history of glaciation, and the shaping of landscapes in glaciated regions.

Reference: Easterbrook, D. J. (1993). “Surface Processes and Landforms.” Prentice Hall.

^DDripstone

Dripstone refers to calcite deposits formed by the dripping of water in caves, commonly seen as stalactites hanging from the ceiling and stalagmites growing from the floor. Dripstones are formed from the precipitation of calcium carbonate as water loses carbon dioxide. They are important in the study of speleology, paleoclimate, and karst environments.

Reference: Ford, D. C., & Williams, P. (2007). “Karst Hydrogeology and Geomorphology.” Wiley.

^DDropstone

A dropstone is an isolated fragment of rock that has been transported by floating ice, such as an iceberg, and deposited in marine or lacustrine sediments. The presence of dropstones in sedimentary layers is an indicator of glacial activity and is important in paleoclimatology and the study of ancient ice ages.

Reference: Andrews, J. T. (2000). “Icebergs and the Greenland Ice Sheet: The Evidence from Radiocarbon Dating.” Quaternary Science Reviews, 19(10), 983-1014.

^DDrumlin

A drumlin is an elongated hill formed by glacial action, composed of till, and shaped like an inverted spoon or half-buried egg, with its long axis parallel to the direction of ice movement. Drumlins are often found in clusters called drumlin fields. Their study provides valuable insights into glacial dynamics, ice flow directions, and the behavior of past ice sheets.

Reference: Benn, D. I., & Evans, D. J. A. (2010). “Glaciers and Glaciation.” Routledge.

^EEarthflow

An earthflow is a type of mass wasting where a mass of earth or fine-grained soil moves downslope under the influence of gravity, often triggered by saturation from rainfall. Earthflows can vary in speed from slow to rapid and are significant in shaping landscapes, especially in hilly or mountainous regions. They are also important in understanding soil stability and landslide hazards.

Reference: Varnes, D. J. (1978). “Slope Movement Types and Processes.” Landslides: Analysis and Control, Transportation Research Board Special Report 176.

^WArchives: Glossary

Well-sorted sediment is a deposit in which the particles are of relatively uniform size, often resulting from the action of wind or water that selectively transports and deposits particles of similar size. Well-sorted sediments are significant in sedimentology for understanding the energy conditions of depositional environments, the processes of sediment transport, and the formation of sedimentary structures.

Reference: Boggs, S. (2009). “Petrology of Sedimentary Rocks.” Cambridge University Press.