Chapter 8: From sediment to sedimentary rock

coalification

process of lithifying coal. Compaction-release of water-slow chemical changes welding the plant fragments together-lower in water and richer in carbon.

Chemical sedimentary rock

results from the lithification of chemical sediment. Mostly only composed of one important mineral e.g: calcite, dolomite, gypsum, halite. Often form as evaporite deposits.

Playas

seasonal lakes, evaporate and deposit salts.

Sand

sediment consisting of particles the size of a pinhead.

Gravel

sediment with pea sized or larger particles.

Sphericity

shaped like a sphere

Major modes of sediment transport

stream transport, glacial transport, mass wasting (gravity), wind transport, longshore transport, turbidity currents, bottom currents

mud cracks

texture forming from the drying out of a riverbed

Ripples

texture forming in shallow water, windy areas, coastal waves- move sand in wavy structures

back arc basin

location of sediment accumulation at convergent plate boundary. Forms on the overriding plate on behind the subduction zone.

diagenesis

low pressure changes that happen to sediment after deposition. Include lithification

Streams and floodplains

main transporters of sediment on land. Sediment carried is better sorted and rounded as distance from source increases.

melange

mix of volcaniclastic sediment, fragments of oceanic lithosphere, and rock metamorphosed under low temperature, high pressure conditions of subduction zone.

Pyroclasts

(fire) clasts ejected from volcano. Classified by size-bombs, lapilli and ash.

deposited

(of water, the wind, or other natural agency) lay down (matter) gradually as a layer or covering.

Peat

A biogenic sediment formed from the accumulation and compaction of plant remains from bogs and swamps, with the carbon content of about 25%

Limestone

A biogenic sedimentary rock that consists primarily of the mineral Calcite. Formed from lithified shells and other skeletal material of marine organism. Argonite ->calcite through diagenesis.

Coal

A combustible rock (50-95% carbon), formed by the compression, heating, and lithification of peat. Process called coalification.

Mudstone

A group of very fine-grained, non-fissile sedimentary rock types with different proportions of silt and clay sized particles. includes rock type siltstone and claystone (distinguished by silt and clay sized particles). breaks into blocky fragments.

Rift Valley

A linear, fold bounded Valley along a divergent plate boundary or spreading center

Evaporite

A rock formed by the evaporation of lakewater or seawater, followed by lithification of the resulting salt deposit. Marine variety make up 30% of the land area of North America

Delta

A sedimentary deposit, commonly triangle shaped, that forms where a Stream enters a standing body of water

Estuary

A semi enclosed body of coastal water, in which freshwater mixes with seawater. Load being carried to sea may be trapped in these. Coarse sediment tends to settle close to land and fine sediment is carried out to sea. Large amounts of organic matter from land and sea can be found here.

Turbidity current

A turbulent, gravity driven flow consisting of a mixture of sediment and water, which conveys sediment from the continental shelf to the deep-sea

Banded iron formation

A type of chemical sedimentary rock rich in iron minerals and silica. Unusual but economically important. 1.8-2.5 billion years old. Brown colour-red=Fe3+, black=Fe2+, white=silica

Shale

A very fine-grained fissile or laminated sedimentary rock, consisting primarily of silt or clay sized particles; a fissile mudstone.

Sedimentary wedges

Accumulation of clastic sediment affected by plate tectonics. Convergent:Accumulate in rift valleys, passive continental margins, structural basins along the edge of mountain ranges. Divergent: deep sea trenches along subduction zones, back arc basin

Marine evaporite basins

Ocean water may evaporate fast enough to leave behind the salts that were dissolved in it.

precipitated

Chemistry cause (a substance) to be deposited in solid form from a solution. • cause (drops of moisture or particles of dust) to be deposited from the atmosphere or from a vapor or suspension.

Conglomerate

Clastic sedimentary rock with large fragments in a finer grained matrix. Must have clasts larger than 2mm

Clastic sedimentary rock

Conglomerate, Sandstone, mudstone, and shale. Equivalents of gravel, sand, silt, and clay rich sediment.

sites of deposition in and near the ocean

Deltas and estuaries, beaches, shelves, carbonate platforms and reefs, marine evaporite basins, turbidites and seafloor.

Till

Glacial sediment consisting of all the types of rock over which the ice passed.

volcaniclastic sediment

Kind of clastic sediment, clasts are volcanic in origin. erupting volcanoes blast out large quantities of fragments. Pyroclasts

Sandstone

Medium grained (.05-2mm) clastic sedimentary rock in which the clast is typically, but not necessarily, dominated by quartz grains.

Shelves

Most of the world's sedimentary rock comes from these. Most sand sized sediment deposited within 5km. Sand will consist mostly of silty or sandy mud containing marine fossils.

Wind

Processes related are eolian. Sediment moved tends to be finer. Grains of sand easily transported. Seacoasts and deserts form sand dunes- well sorted grains with bedding inclined in downwind direction 33 degrees.

Beaches

Quartz is a typical component of the sand on these. Sediment tends to be better sorted than in a stream. particles are dragged back and forth by the surf and turned over and over and are rounded by abrasion.

Compaction

Reduction of pore space in the sediment as a result of the weight of overlying sediment. Buried by accumulation of more sediment or by tectonic processes. Cementation or recrystallization then occurs.

Sediment: Gravel = Rock?

Rock: Conglomerate = Sediment?

Sediment: Sand = Rock?

Rock: Sandstone = Sediment?

Sediment: Clayey mud = Rock?

Rock: Shale or Mudstone = Sediment?

Sediment: Silty mud = Rock?

Rock: Siltstone = Sediment?

Lakes

Sediment deposited accumulates on shore and floor. Deltas (inclined well sorted layers on the front pass down and out into thinner, finer grained, evenly laminated layers) formed from diminishing velocity of feeder stream. Seasonal playas can be formed

Chemical sediment

Sediment formed by the precipitation of minerals dissolved in lakewater, river water, or seawater. Can happen in two ways:plants and animals living in water can change chemical balance and cause precipitation or an inland sea dries up. Example: Utah's Bonneville Salt flats

Clastic sediment

Sediment formed from fragmented rock and mineral debris produced by weathering and erosion. derives name from clasts (individual grains of mineral or fragments of rock). Characteristics used to describe are size range of grains, shape, angularity.

Siliceous ooze

Sediment from silica secreting organisms. Chemically similar to quartz but differs in mineral structure. Common in equatorial Pacific and Indian oceans and in belt around Antarctic. Areas of high biologic productivity.

Glaciers

Sediment is deposited along the base or at the margins. May be reworked by running water. Creates sediment called till.

eolian sediment

Sediment that is carried and deposited by wind

Biogenic sediment

Sediment that is primarily composed of plant and animal remains or that precipitates as a result of biologic processes. Include the hard part of animals like bones, shells and teeth and plant matter like wood, roots and leaves. Common rocks are limestone (from calcium carbonate skeletons of marine invertebrates) and coal (from partially decomposed terrestrial plant material).

Silt

Sediment with particles ranging in size between those of sand and clay. roughly table salt grain size.

Clay

Sediment with the finest sedimentary particles, the size of flour or smaller.

Sites of deposition on land

Stream valleys, lakes, adjacent to glaciers and wherever winds blow and pick up sediment.

Recrystallization

The formation of new crystalline mineral grains from old ones. Pressure causes less stable minerals to rearrange crystals into more stable forms. Aragonite present in skeletal structures of living corals and other marine invertebrates. Aragonite->calcite with a different crystalline structure.

Lithification

The group of processes by which loose sediment is transformed into sedimentary rock.

Bedding

The layered arrangement of strata in a body of sediment or sedimentary rock. Banded appearance from sedimentary rock being deposited in distinct strata.

Deposition

The laying down of sediment. Occurs wherever the carrying capacity (energy) of the transporting agent decreases sufficiently for sediment to settle out. example: stream channels and flood planes, lakeshores and lake bottoms, the margins of glaciers, where wind is intermittently strong like beaches and deserts.

cementation

The process in which substances dissolved in pore water precipitate out and form a matrix in which grains of sediment are joined together. Weight of accumulating sediment forces grains together, reducing pore space and forcing water out of sediment->as water rises and cools, ions dissolved in water precipitate(silica, calcium carbonate, iron hydroxide), forming minerals that cement the grains together.

Bedding surface

The top or bottom surface of a rock stratum or bed. The boundary between adjacent strata. can tell geologist about how the sediment was deposited.

Turbidites

Thick sediment deposits found at the foot of the continental slope, depths as great as 5km. Caused by turbidity currents, underwater landslides. Sometimes started by the shaking of earthquakes- rush up to 90km/h- slows down and deposits this sediment

Poorly sorted sediment

a jumble of particles of different sizes of sediment, usually transported by ice or mass wasting. Example: Till-ice transported sediment from glaciers

Breccia

angular clasts in a conglomerate. Means sediment transported short distance.

chert

biogenic rock consisting of tiny particles of quartz from shells of microscopic marine animals.

dolostone

biogenic rock formed when calcite is replaced by dolomite(calcium and magnesium)

Calcareous ooze

biogenic sediment on seafloor that is made of calcium carbonate and comes from the remains of tiny sea creatures. Shells sink to bottom, in warm waters.

Cross bedding

caused by turbulent flow in streams, wind or ocean waves. Thick strata of sandstone contain thick beds that are inclined with respect to stratum in which they occur. Can tell geologists of direction of water, wind. Example: Utah's Zion national park

sedimentary facies

changes in the character of sediment from one environment to another. May be distinguished from one another by different grain sizes, grain shape, stratification, colour, chemical composition, depositional structure, or fossils. May blend into each other or end abruptly.

graded bed

coarse clasts are concentrated at the bottom, grading up to the finest on top. Often where a stream or river enters a lake or ocean.

fissile

easily split. describes shale that splits into sheet like fragments.

Angular

edges or corners jagged. Seen in ice erosion

Roundness

edges or corners smooth. Caused by water or wind erosion

Matrix

finer grained material surrounding clasts in conglomerate.

Delta deposits

form where streams flow into lakes or seas. In marine environments they are complex and consist of coarse stream channel sediment, fine sediment deposited between channels and still finer sediment deposited on the seafloor.

sodium carbonate, borax

formed by the evaporation of lake water.

Calcite, gypsum, halite

formed by the evaporation of seawater.

ophiolites

fragments of oceanic lithosphere incorporated into the melange. Expose oceanic crust and underlying mantle at the surface.

Well sorted sediment

in sediment all the particles are nearly the same size. Usually transported by water or wind. Example: Quartz sand

carbonate platforms

the top of a pillar of limestone deposited by years of coral and other marine debris accumulating. Light blue platform seen off Floridian islands. Accumulation of biogenic sediment on continental shelves .

Reef

wave resistant structure built from the skeletons of marine invertebrates. Generally restricted to warm, sunlit waters of normal marine salinity.

accretionary wedge

wedge-shaped accumulations of volcaniclastic sediment. Example: Islands of Taiwan and Barbados.

Alluvial fan

when a mountain stream reaches the bottom and is no longer constricted by valley walls it spreads out and deposits sediment. Larger more angular and poorly sorted gravel is deposited higher up where the current is strong, and well sorted sand is deposited downstream.

loess

windblown dust transported from desert surfaces, glacial sediment and glacial stream deposits at time of ice sheet retreat.