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Chapter 6: Sedimentary Rocks
Terms in this set (60)
Sediment (pg. 128)
Loose, solid particles that can originate by (1) weathering and erosion of preexsiting rocks (detrital sediments), (2) chemical precipitation from solutions, usually water, and (3) secreation by organisms (chemical sediments).
Gravel (pg. 129)
All rounded particles coarser than 2 millimeters, the thickness of a nickel. (Angular fragments of this size are called rubble.)
Pebbles (pg. 129)
Particles ranging from 2 to 64 millimeters in size. (About the size of a tennis ball.)
Cobbles (pg. 129)
Particles ranging from 64 to 256 millimeters (About the size of a basketball.)
Sand (pg. 129)
Grains from 1/16 millimeter to 2 millimeters in diameter. Grains of this size are visible and feel gritty between fingers.
Silt (pg. 129)
Grains from 1/256 millimeter to 1/16 millimeter. (Feels gritty on teeth.)
Clay (pg. 129)
The finest kind of sediment at less than 1/256 millimeter. Mud is a loose term used to describe a mixture of silt and clay. Clay particles can be composed of any mineral.
Transportation (pg. 129)
The movement of eroded particles by agents such as rivers, waves, glaciers, or wind.
Rounding (pg. 129)
The grinding away of sharp edges and corners of rock fragments during transportation. Rounding occurs in sand and gravel as rivers, glaciers, or waves cause particles to hit and scrape against one another or against a rock surface.
Sorting (pg. 129)
The process by which sediment grains are selected and separated according to grain size (or grain shape or specific gravity) by the agents of transportation, especially by running water.
Deposition (pg. 130)
The settling or coming to rest of transported material.
Environment of Deposition (pg. 130)
The location in which deposition occurs, usually marked by characteristic physical, chemical, or biological conditions. (Examples; deep-sea floor, a desert valley, a river channel, a coral reef, a lake bottom, a beach and a sand dune.)
Lithification (pg. 131)
The general term used for the processes that convert loose sediment into sedimentary rock Most of these rocks are lithified by a combination of compaction & cementation.
Pore Space (pg. 131)
The total amount of space taken up by openings between sediment grains.
Compaction (pg. 131)
A loss in overall volume and pore space of a rock as the particles are packed closer together by the weight of overlying material.
Cement (pg. 131)
The solid material that precipitates in the pore space of sediments, binding the grains together to form solid rock.
Cementation (pg. 131)
The chemical precipitation of material in the spaces between sediment grains, binding the grains together into a hard rock.
Clastic Texture (pg. 132)
A sedimentary rock that consists of sediment grains bound by sediment into a rigid framework. Usually such a rock still has pore space because cement rarely fills the pores completely.
Crystallization (pg. 132)
Some sedimentary rocks form this way through the development and growth of crystals by precipitation from solution at or near the Earth's surface.
Crystalline Texture (pg. 132)
An arrangement of interlocking crystals that develops as crystals grow and interfere with each other. Crystalline rocks lack cement because they are held together by the interlocking crystals. These rocks have minimal pore space.
Sedimentary Rocks (pg. 132)
Rocks formed fro (1) eroded mineral grains, (2) minerals precipitated from low-temperature solution, or (3) consolidation of the organic remains of plants. These different types of sedimentary rock are called; detrital, chemical and organic rocks.
Detrital Sedimentary Rocks (pg. 132)
Most common sedimentary rock group, they're composed of fragments of preexisting rock; sedimentary breccia, conglomerate, sandstone & shale. Three are composed of clasts (broken pieces) of mineral derived from the erosion of land.
Chemical Sedimentary Rocks (pg. 132)
A rock composed of material precipitated directly from solution. Chemical precipitation can also be caused by organisms; limestone, dolomite & chert. They are precipitated either directly by inorganic processes or by the actions of organisms.
Organic Sedimentary Rocks (pg. 132)
Rocks composed of organic carbon compounds, such as plant remains; coal.
Sedimentary Breccia (pg. 132)
A coarse-grained detrital sedimentary rock formed by the cementation of coarse, angular fragments of rubble. This type of rock is not particularly common.
Conglomerate (pg. 132)
A coarse-grained detrital sedimentary rock formed by the cementation of rounded gravel. It can be distinguished from breccia by the definite roundness of its particles.
Sandstone (pg. 133)
A medium grained detrital sedimentary rock (grains between 1/16 and 2 millimeters) formed by the cementation of sand grains. Any deposit of sand can lithify into sandstone.
Quartz Sandstone (pg. 133)
A sandstone in which more than 90% of grains are Quartz. Grains are usually well sorted and well-rounded because they have been transported for great distances.
Arkose (pg. 133)
A sandstone with more than 25% of grains consisting of feldspar. Most of these sandstones contain coarse, angular grains. May have been deposited with an alluvial fan.
Alluvial Fan (pg. 133)
A large, fan-shaped pile of sediment that usually forms where a steam emerges from a narrow canyon onto a flat plain at the the foot of a mountain range.
Martix (pg. 133)
Fine-grains material found in the pore space between larger sediment grains. Sandstone may contain a substantial amount of this in the form of fine-grained silt and clay in the space between larger sand grains.
Graywacke (pg. 133)
A type of sandstone in which more than 15% of the rocks volume consists of fine-grained matrix. They are commonly hard and dense, and they are generally dark gray or green. The sand grains in the rock typically consist of Quartz, feldspar, and sand-sized fragments of other sedimentary, volcanic and metamorphic rocks.
Shale (pg. 133)
A fine-grained detrital sedimentary rock notable for its ability to split into layers. Most of these rocks contain both silt and clay and are so fine-grained that the surface of the rock feels VERY smooth. Lithification of these rocks accumulate on lake bottoms, ends of river deltas, river flood plains, and on quiet parts of the deep-ocean floor.
Siltstone (pg. 134)
A detrital sedimentary rock consisting mostly of silt grains. It's somewhat more coarse-grained than most shales. It lacks the fissility and laminations of shale.
Claystone (pg. 134)
A detrital sedimentary rock that is composed predominantly of clay-sized particles but lacking the fissility of shale.
Mudstone (pg. 134)
A detrital sedimentary rock containing both both silt and clay, having the same grain size and smooth feel of shale but lacking shale's laminations and fissility. It's massive and blocky, while shale is visibly layered and fissile.
Limestone (pg. 136)
A chemical sedimentary rock composed mostly of calcite. They are precipitated either by the actions of organisms or directly as the result of inorganic processes. There are two major types; biochemical and inorganic.
Biochemical Limestone (pg. 136)
A chemical sedimentary limestone rock that is precipitated through the actions of organisms. Mostly formed on continent shelves in warm shallow sea water. Can also be precipitated directly in the core of a reef by corals, encrusting algae, or other shell forming organisms. Such a rock would contain the fossils remains of organisms persevered in growth position.
Coquina (pg. 137)
A variety of biochemical limestone that forms from the cementation of shells and shell fragments that accumulated on the shallow sea floor near the shore. It has a clastic texture and is usually coarse-grained with easily recognizable shells and shell fragments in it.
Chalk (pg. 137)
A light colored, porous, very fine-grained variety of bioclastic limestone that forms from the sea-floor accumulation of microscopic marine organisms that drift near the sea surface.
Ooltic Limestone (pg. 137)
A distinctive variety of inorganic limestone formed by the cementation of sand-sized oolids, small spheres of calcite inorganically precipitated in warm shallow sea water. It has a clastic texture.
Tufa & Travertine (pg. 137)
Inorganic limestones that form from fresh water. Tufa is precipitated from solution in the water of a continental spring or lake, or from percolating ground water. Travertine may form in caves when carbonate-rich water loses its carbon to the cave atmosphere. Both have a crystalline texture.
Recrystallization (pg. 137)
The process by which new crystals, often of the same mineral composition as the original grains, develop in a rock.
Dolomite or Dolostone (pg. 139)
A chemical sedimentary rock composed mostly of the mineral dolomite. Forms as a replacement for existing carbonate material or when pressure and temperature and pressure increase as a result of basin subsidence and deep burial of the carbonate sediment.
Chert (pg. 140)
A hard, compact, fine-grained chemical sedimentary rock formed almost entirely of silica. It occurs in two principle forms; as irregular lumpy nodules within other rocks and as layered deposits like other sedimentary rocks.
Evaporates (pg. 142)
Chemical sedimentary rocks formed from crystals that precipitate during the evaporation of water. They form from the evaporation of sea water or a saline lake. Common evaporates are rock gypsum and rock salt and they have a crystalline texture.
Coal (pg. 142)
A organic sedimentary rock that forms from the compaction of plant material that has not completely decayed. Plant fossils in coal beds include leaves, stems, tree trunks with roots often extending into the underlying shales.
Sedimentary Structures (pg. 143)
A feature found within sedimentary rocks, usually formed during or shortly after deposition of the sediment and before lithification.
Bedding (pg. 143)
A series of visible layers within rock. One the most prominent structures seen in most large bodies of sedimentary rock.
Original Horizontality (pg. 143)
The first principle of straightgraphy that states most water-laid sediment is deposited in horizontal or near horizontal layers that are essentially parallel to the Earth's surface.
Bedding Plane (pg. 143)
A nearly flat surface of deposition separating two layers of rock. A change in grain size or composition or the particles being deposited, or a pause during deposition, can create bedding planes.
Cross-Bedding (pg. 143)
An arrangement of relatively thin layers of rock inclined at an angle to the more nearly horizontal planes of the larger rock unit. They form one after another.
Ripple Marks (pg. 143)
Any of the small ridges formed on sediment surfaces exposed to moving wind or water. The ridges form perpendicularly to the motion.
Graded Bed (pg. 147)
A layer with a vertical change in particular size, usually from coarse grains at the bottom of the bed to progressively finer grains at the top.
Turbidity Current (pg. 147)
A turbulently flowing mass of sediment-laden water that is heavier than clear water and therefore flows downslope along the bottom of the sea or lake. They're considered underwater avalanches and are typically triggered by earthquakes or submarine landslides.
Mud Cracks (pg. 147)
A polygonal pattern of cracked formed in very fine-grained sediment as it dries. Because drying requires air, they only form in sediment exposed above water.
Fossils (pg. 147)
Traces of plant or animal remains preserved in sedimentary rock.
Formation (pg. 149)
A body of rock of considerable thickness that is large enough to be mappable, and with characteristics that distinguish it from adjacent rock units.
Contact (pg. 149)
A boundary or surface between two different rock types or ages of rock, in sedimentary rock formations, the contacts are usually bedding planes.
Source Area (pg. 150)
The locality that eroded to provide sediment to form a sedimentary rock.
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