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Geology Ch 6
Terms in this set (35)
produced from weathering products of preexisting rocks or accumulated biological matter (remains of plants and animals)
produced from rock fragments
• most common sedimentary rock type
• form from cemented sediment grains that come from pre-existing rocks
produced by precipitation of dissolved ions in water
• crystalline textures
• form by precipitation of minerals from solution
produced by accumulation of biological debris, such as in swamps or bog
• accumulate from remains of organisms
Loose, solid particles originating from
• weathering and erosion of pre-existing rocks
• chemical precipitation from solution, in many cases aided by living organisms in water
• Movement of sediment away from its source, typically by water, wind, or ice
• Rounding of particles occurs due to abrasion during transport
• Sorting occurs as sediment is separated according to grain size by transport agents, especially running water
• Settling of transported material
• Accumulation of chemical or organic sediments, typically in water
• Environment of deposition is the location in which deposition occurs
• deep sea floor
• desert dunes
• river channel
• lake botto
• sediment must be preserved, by burial with additional sediments, in order to become a sedimentary rock
• General term for processes converting loose sediment into sedimentary rock
• Combination of compaction and cementation
When groundwater moves through pore spaces, when certain conditions are met, some minerals (usually calcite or quartz) precipitates and gradually fills up the pore spaces and bind the grains.
Breccia and Conglomerate
• coarse-grained clastic sedimentary rocks
• breccia composed of coarse, angular rock fragments
• conglomerate composed of rounded gravel
• medium-grained clastic sedimentary rock
• types determined by composition
o quartz sandstone - >90% quartz grains
o arkose - mostly feldspar and quartz grains
o graywacke - sand grains surrounded by dark, fine-grained matrix, often clay-rich
Fine-grained clastic sedimentary rock; tends to split into thin layers (fissility)
• silt- and clay-sized grains
• sediment deposited in lake bottoms, river deltas, floodplains, and on deep ocean floor
More fined grained-rocks
•Siltstone - slightly coarser-grained than shale; non-fissile •Claystone - predominantly clay-sized grains; non-fissile •Mudstone- silt- and clay-sized grains; massive/blocky
• Contain CO32- as part of their chemical composition
• Most are biochemical, derived from dead remains of animals such shells and corals, and algae.
• Limestone is composed mainly of calcite (CaCO3).
• Chemical alteration of limestone in Mg-rich water solutions can produce dolostone (dolomite is the mineral)
• Chalk is a very fine-grained biochemical limestone
• hard, compact, fine-grained, formed almost entirely of silica
• can occur as layers or as lumpy nodules within other sedimentary rocks, especially limestone
• Flint is a subcategory of chert.
Sediments made of crystals that precipitate when saline water of lakes and oceans evaporate.
sedimentary rock forming from compaction of partially decayed plant material
• organic material deposited in water with low oxygen content (i.e., stagnant)
Series of visible layers within a rock. Most common sedimentary structure
A (sedimentary) rock body of considerable thickness that is large enough to be mapped. One formation may consists of multiple beds
•Often based on rock type •Must have a visible characteristic that makes it a recognizable unit
•A formation is usually named after the geographic area where it is exposed on the surface and the rock type
a boundary surface between two different rock types or ages of rock.
Geologic history of an area source area
• The locality where the rock was weathered, eroded and provided sediment.
• Sediment composition is an indicator of the type of rock from which the sediments come from.
• Shape, size and sorting are indicators of how far the sediments may have been transported from the source area.
Environment of Deposition
The composition, shapes, size of the sediments, their distribution patterns, layering, etc. gives geologists clues on what kind of environment the sediments deposited.
It occurs where a river comes out of a mountain and its flow slows down suddenly. Mountains often have granite as their bedrock. In such cases, the sediments are rich in quartz and feldspars. The deposits are relatively close to the source area. Thus, there may be large sediment pieces in the mix
River Channel and Flood Plain Rivers
deposit elongated lenses of sediments, typically sandstone. A flood plain is a flat land next to a river, where it becomes flooded from time to time. Sediments on flood plains tend to consist of finer grains than those on the river bottom.
A delta is a body of sediment located at the mouth of a river, where the river meets an ocean or a lake. Deltas are often triangular in shape. Because a delta is farthest away from the source area, its sediments tend to be finegrained sediments such as silt and mud.
Beaches, Dunes, and Barrier Islands
A large portion of the sediments transported by rivers to an ocean are redistributed along the shoreline by currents and waves. In wide, sandy beaches, sand dunes may form. A barrier island is an elongated pile of sands that are oriented parallel to the shoreline.
Abyssal Fan (Submarine Fan)
A fan-shaped body of sediments deposited on deep seafloor. Usually located at the lower end of a submarine canyons, through which sediments deposited near-shore are transported down
When sea level rises, the shoreline migrates inland. So the location of sediment deposition also moves inland
When sea level falls, the shoreline shifts toward the ocean. So does the location of sediment deposition
• series of thin, inclined layers within a horizontal bed of rock
• found in sandstones deposited in ripples, bars, dunes, deltas
Wavy forms on the surface of a sediment layer created by moving wind or water.
• polygonal cracks formed in drying mud
• traces of plants or animals preserved in rock
• hard parts (shells, bones) of animals that turned into rock.
• Fossils tell geologists what types of animals and plants were there when and where the sediments were deposited. Therefore, they are useful in inferring the environment in which they deposited.
• What are the three types of sedimentary rocks?
• How are detrital sediments classified (grouped)?
• How do detrital sediments turn into rocks?
• What happens to detrital sediments while they are transported away from the source area by running water?
• How are chemical sediments created ?
• What types of sedimentary structures can be observed?
• In what types of environment do detrital sediments deposit?
• How do geologists infer the environment in which sediments were deposited?
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