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Structured Geological Glossary: Sedimentary Rocks

sediment Rock debris commonly produced by mechanical or chemical weathering processes.
sedimentary Sedimentary rocks are formed from pre-existing rocks or pieces of once-living organisms. They form from deposits that accumulate on the Earth’s surface. Sedimentary rocks often have distinctive layering or bedding.
sedimentary A rock formed by the accumulation and cementation of mineral grain transported by wind, water, or ice to the site of deposition or chemically precipitated at the depositional site.
sedimentation The process of deposition of mineral grain or precipitates in bed or other accumulations. Seif dune
sedimentary petrology Study of the composition, characteristics and origin of sediment and sedimentary rocks.
surficial deposit Any loose, unconsolidated sedimentary deposit lying on bedrock.
deposition A general term for the accumualtion of sediment by either physical or chemical sedimentation.
bedding Sedimentary layer in a rock. The bed are distinguished from each other by grain size and composition, such as in shale and sandstone. Subtle changes, such as beds richer in iron-oxide, help distinguish bedding. Most beds are deposited essentially horizontally. A characteristic of sedimentary rocks in which parallel planar surfaces separating different grain sizes or compositions indicate successive depositional surfaces that existed at the time of sedimentation.
bed A distinct sedimentary layer (stratum) thicker than 1 centimeter.
stratification A structure of sedimentary rocks, which have recognizable parallel bed of considerable lateral extent.
flaggy Term used to describe sedimentary or metamorphic rocks that tend to split into layer that are 1-10 cm thick.
well-sorted Refers to a sedimentary deposit or rock with grain of the same approximate size.
turbidire The sedimentary deposit of a turbidity current, typically showing graded bedding and sedimentary structure on the undersides of the sandstone.
terrestrial planet "A planet similar in size and composition to the Earth; especially Mars, Earth, Venus, and Mercury. "
terrestrial A deposit of sediment that accumulated above sea level in lakes, alluvial fans, floodplains, moraine, etc., regardless of its present elevation.
fluvial sediment Sediment deposited by the flowing water of a stream.
graded bedding A bed in which the coarsest particles are concentrated at the bottom and grade gradually upward into fine silt, the whole bed having been deposited by a waning current.
topset bed A horizontal sedimentary bed formed at the top of a delta and overlying the foreset beds.
paleocurrent map A map of depositional currents that have been inferred from cross-bedding, ripple, or other sedimentary structure.
paleowind A prevailing wind direction in an area, inferred from dune structure or the distribution of volcanic ash for one particular time in geologic history.
forset bed " One of the inclined bed found in crossbedding; also an inclined bed deposited on the outer front of a delta. "
ripple A very small dune of sand or silt whose long dimension is formed at right angles to the current.
compositional maturity "Extent to which a clastic sediment approaches the compositional end product of chemical weathering; the extent to which the most stable components of a sediment have been enriched over unstable components. In sandstone, compositional maturity can be conveniently expressed in terms of the abundance of quartz the most stable common phase in most sandstones."
sedimentary structure "Any structure of a sedimentary or weakly metamorphosed rock that was formed at the time of deposition; includes bedding, cross-bedding, graded bedding, ripple, scour marks, mud-cracks. "
oscillation ripple A ripple with a symmetrical cross section and a sharp peak formed by wave.
swash The landward rush of water from a breaking wave up the slope of the beach.
compaction Occurs when the weight of overlying material compresses more deeply buried sediment. Along with cementation, this process converts sediments to solid rock.
unconsolidated Loosely arranged, not cemented together, so particles separate easily.
lithification The conversion of loose sediment into solid sedimentary rock. Several processes, including compaction of grain, filling of spaces between grains with mineral cement, and crystallization act to solidify sediment.
cementation The lithification of sediment by the precipitation of mineral from watery solutions percolating through the sediment.
calcrete A surficial gravel and sand conglomerate cemented by calcium carbonate.
diagenesis A group of processes that cause physical and chemical changes in sediment after it has been deposited and buried under another layer of sediment. Diagenesis may culminate in lithification of sediment, turning it into solid rock.
concretion A hard nodular structure formed in sediment or in a sedimentary rock by diagenesis.
authigenesis Process by which new mineral form in place within a sediment during deposition or in the early stage of diagenesis.
lithology The systematic description of rocks, in terms of mineral composition and texture.
argillite Name used for unusually hard, fine-grained sedimentary rocks, such as shale, mudstone, silttone, and claytone. Commonly black.
argillic horizon A clay-rich layer of soil. Clay often form in overlying soil layers from the decomposition of feldspar and other minerals. The extremely fine clay particles are gradually carried down by water to accumulate into the argillic horizon.
argillaceous A term used to describe clay-rich rocks.
clast A solid product of erosion. Clasts are sometimes referred to as detritus or detrital material.
clastic Pertaining to a rock or sediment composed principally of fragmental detrital materials.
clastic rock A sedimentary rock formed from mineral particles (clasts) that were mechanically transported.
detrital sediment A sediment deposited by a physical process.
sapropel "Lithified organic-rich marine sediment deposited under anoxic conditions. If the organic content is very high, the sediments lithify to become black shale; if dilution by clay or other materials occurs, the sediments lithify to become marlstone."
evaporite A chemical sedimentary rock consisting of mineral precipitated by evaporating waters, especially sal and gypsum.
chemical sedimentary rock Sedimentary rock composed of mineral that were precipitated from water. This process begins when water traveling through rock dissolves some of the minerals, carrying them away from their source. Eventually these minerals are redeposited, or precipitated, when the water evaporates away or when the water becomes over-saturated.
mineral precipitate A mineral deposited from a water solution in pores or other openings in rocks. Chemical reaction with the surrounding rock, changes in pressure or temperature, or just drying up (evaporation) can cause a mineral to precipitate out of solution. Quartz vein are common products of mineral precipitation.
limestone A sedimentary rock made mostly of the mineral calcite (calcium carbonate). Limestone is usually formed from shells of once-living organisms or other organic processes, but may also form by inorganic precipitation.
limestone A sedimentary rock made mostly of the mineral calcite (calcium carbonate CaCO2). Limestone is usually formed from shells of once-living organisms or other organic processes, but may also form by inorganic precipitation.
travertine A terrestrial deposit of limestone formed in cave and around hot spring where cooling, carbonate-saturated groundwater is exposed to the air.
bird's-eye limestone Layered limestone that is full of holes some of which may have been secondarily filled by cementing mineral. The holes were produced by burrowing animals or by gas bubbles. Most of these limestones are of intertidal or supratidal origin.
carbonate rock A sedimentary rock that consists primarily of carbonate mineral. The dominant mineral is nearly always either calcite, in which case the rock is limestone, or dolomite, in which case the rock is dolomite.
carbonate sediment Unconsolidated sediment that consisls primarily of carbonate mineral, usually aragonite or calcite.
calcareous A descriptive term used for rocks and other earth materials that have an abundance of calcium carbonate (CaCO3). For example, a calcareous sandstone has up to 50% calcium carbonate.
carbonate rocks General term for limestone and dolostone.
coccolith One of the many armorlike plate that surround single-celled marine algae known as coccolithophores.
oolite A sedimentary carbonate particle composed of spherical grain precipitated from warm ocean water on carbonate platform. Also a rock composed of such particles.
lamination Very thin layer of less than 1 cm thickness.
chert An impure rock, often gray in color, that consists primarily of extremely small quartz crystal precipitated from water solutions.
ribbon chert Chert and shale in thin alternating bed. The beds resemble parallel ribbons stretched over an outcrop.
radiolarian chert A rock made up of the spherical siliceous shells of radiolarian which are single-celled planktonic animals (protozoans).
radiolarian Radiolarians are microscopic, single-celled animals that have existed in the ocean throughout the Phanerozoic Eon. . Although they are closely-related to the blob-like amoebas you see in high school biology class, radiolarian are exceptionally elegant creatures. Radiolarians have elaborate skeletons made mostly of silica. They extract the silica from the sea water they live in. They catch their food as they float in the ocean currents by sticking long, sticky, finger-like projections called pseudopodia through the many holes in their skeleton.
After they die, their skeletons may sink to the ocean bottom. If a thick enough layer of skeletons accumulates, they may eventually harden to form chert, a very hard, often colorful, rock.
pelagic sediment Deep-sea sediment composed of fine-grained detritus that slowly settles from surface waters. Common constituents are clay, radiolarian ooze, and foraminiferal ooze.
siliceous Generally refers to a rock rich in quartz.
sandstone A detrital sedimentary rock composed of grain from 1/16 to 2 millimeters in diameter, dominated in most sandstone by quartz, feldspar, and rock fragments, bound together by a cement of silica, carbonate, or other mineral or a matrix of clay minerals.
quartzose sandstone (1) A quartz arenite.
(2) A clean quartz sandstone, less pure than a quartz arehire, that may contain a moderate amount of other detrital mineral and/or calcite cement.
quartzite (1) A very hard, clean, white metamorphic rock formed from a quartz arenite sandstone. (2) A quartz arenite containing so much cement that it resembles ( 1 ). (3) A nonfoliated metamorphic rock formed from pure, dominantly quartz sandstone. (4) Hard, somewhat glassy-looking rock made up almost entirely of quartz. Metamorphosed quartz sandstone and chert are quartzite.
quartz arenite "A sandstone containing very little except pure quartz grain and cement. When cemented by a secondary silica it is named quartzite; an orthoquartzite."
orthoquartzite A clastic sedimentary rock consisting almost entirely of silica cemented quartz grain. The rock has few, if any, heavy mineral or fossil.
arkose A variety of sandstone containing abundant feldspar and quartz, frequently in angular, poorly sorted grain.
conglomerate A rock consisting of rounded clast of gravel surrounded by sand.
breccia A rock that resembles conglomerate in consisting of clast of gravel surrounded by sand, but in breccia the clasts are angular, whereas in conglomerate they are rounded.
sand Loose particles of rock or mineral (sediment) that range in size from 0.0625 - 2.0 millimeters in diameter.
gravel All sedimentary particles larger than two millimeters is called gravel. Gravel is subdivided into pebble, cobble, and boulder.
pebble Loose particles of rock or mineral (sediment) that range in size from 2 - 64 millimeters in diameter. Pebbles are the smallest type of gravel.
cobble A piece of gravel between 8 and 256 millimeters in size.
boulder A piece of gravel larger than 256 millimeters (~10 inches) in size.
clay "Any of a number of hydrous aluminosilicate mineral formed by weathering and hydration of other silicates; also, any mineral fragment smaller than 1/255 mm."
autochthonous clay Clay originating in the soft sediment or sedimentary rock where it is identified and where it formed either by neoformation (i.e., from dissolved elements) or by transformation (i.e., from mineral growth on preexisting sedimentary substrate).
shrink-swell Refers to the property of many clay to swell when wetted and shrink when dried.
allochthonous clay Clay originating in an environment different from the final sedimentary environment (rocky substrate soil or upstream sediment subjected to erosion).
clay-sized sediment Sediment in which particles are smaller than 1/256 millimeter. Most sediment of this size belongs to the clay mineral family.
shale Sedimentary rock derived from mud. Commonly finely laminated (bedded). Particles in shale are commonly clay mineral mixed with tiny grain of quartz eroded from pre-existing rocks. Shaley means like a shale or having some shale component, as in shaley sandstone.
claystone A sedimentary rock that consists primarily of clay but that is not fissile like shale.
mudstone A very fine-grained sedimentary rock formed from mud.
silt Loose particles of rock or mineral (sediment) that range in size from 0.002 - 0.0625 millimeters in diameter. Silt is finer than sand, but coarser than clay.
mud Wet clay and silt-rich sediment.
siltstone A sedimentary rock made mostly of silt-sized grain.
pelite A fine-grained sedimentary rock consisting mostly of clay and/or silt. Mudstone, shale, siltstone, and claystone are all pelitic.
iron formation "A sedimentary rock containing much iron, usually more than 15 percent as sulfide, oxide, hydroxide, or carbonate; a low-grade ore of iron. "
banded iron ore A sediment consisting of layer of chert alternating with bands of ferric iron oxides (hematite and limonite) in valuable concentrations.
banded iron formation An iron formation that consists of alternating iron-rich and iron-poor layer. Most rocks of this type are older than about 2 billion years.
veneer A thin, widespread layer of sediment covering an older surface.
humus The decayed part of the organic matter in a soil.
cross section, geologic A cross-section is a drawing representing a portion of the Earth in a vertical plane.
precipitate (verb) The process that separates solid from a solution.
(noun) Mineral precipitate. A mineral deposited from a water solution in pores or other openings in rocks. Chemical reaction with the surrounding rock, changes in pressure or temperature, or just drying up (evaporation) can cause a mineral to precipitate out of solution. Quartz vein are common products of mineral precipitation.
diatomite A siliceous chert-like sediment formed from the hard parts of diatom.
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