Sedimentary RocksSedimentary RocksSediments form layers, called strataSediments form layers, called strata

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Ions weather out of rock,are transported bygroundwater to sediment layers below

Ion-richground-water

Ions transportedto lake or ocean

Dissolved ions precipitateto form cement betweensediment grains

Water enters pore spaces between sediment grains

Sediment grains moved to ocean by streams

LITHIFICATIONCompaction and Cementation

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Particles are large andirregular, and consist ofa variety of lithologies,including the leastresistant.

Particles are mid-sizedand of intermediatesphericity, and includeresistant and nonresistantlithologies.

Particles are small andnearly spherical, andconsist mainly of themost resistant lithologies,such as quartz.

Character of detrital sediments depends on time, distance, and energy. For example, in streams:

HIGHLANDS LOWLANDS NEAR-COASTAL

Sedimentary environment determines roundness sorting, mineral diversity

Examination of minerals present and their sorting, angularity, size and cements reveal the distance

from the source and local chemistry

Remember: sand 0.063 – 2mmGravels coarserMuds less

Remember: sand 0.063 – 2mmGravels coarserMuds less

500 mm = .5 mm log base 2 of .5 is -1500 mm = .5 mm log base 2 of .5 is -1-1 x -1 is 1-1 x -1 is 1

http://logbase2.blogspot.com/2008/08/log-calculator.html

Wadell roundness

Dott: % mud matrix

Dott: % mud matrix

Dott: % mud matrix

Sparry cement: clear, relatively coarse-grained calcite in the interstices of any sedimentary rock

Micrite is a term used to describe lime mud, carbonate of mud grade. The term is also used in the Folk classification to describe a carbonate rock dominated by fine-grained calcite.

Folk: bound by mud or precipitated calcite

restrain or regulate

When bound:

When bound:

MaturityMaturity• Blatt and Tracy page 232 • Recall that weathering makes

smaller grains, and chemical weathering, especially hydrolysis, dissolves feldspars and micas leaving clays, metal ions, and dissolved silica.

• Quartz is not effected except for fragmentation and rounding.

• Thus a granite or granodiorite, or compositionally equivalent metamorphic rock, leaves behind quartz and clay.

Ions and molecules in aqueous solution are the raw materials fro cements

TransportTransport

• The clays are FLAT microcrystals and spend much of their time in suspension. Most end in deep marine sediments over the long run. DEMO sheet of paper

• Quartz fragments generally travel in the bed load, so they are deposited, and frequently buried, in a variety of non-marine and marine environments, preserving less

common environments

Without rift valleys, we wouldn’t know much about our own past.

AngularityAngularity

Using these ratios then you can apply a name according to Folk (1974):Under 0.60 very elongate0.60 to 0.63 elongate0.63 to 0.66 sub-elonate0.66 to 0.69 intermediate shape0.69 to 0.72 sub-equant0.72 to 0.75 equantOver 0.75 very equant

http://people.uncw.edu/dockal/gly312/Fall2009/Labs/02Observation%20and%20Description%20of%20Graons.htm

Grains become more rounded with time in transport

Fine sediments need still water to settle

What fills the spaces between grains?

Graywacke with matrix Sandstone with hematite cement

Compaction (some dewatering) and cementation

Diagenesis:

Micritic – very fine grained; Acicular – needle like; Drusy - aggregate of minute crystals coating a surface

poikilotopic a crystalline sedimentary rock having multisized crystals, the larger of which enclose small ones, often of a different mineral

Cements often control appearance

Sometimes Quartz from volcanic rocks (e.g. from Rhyolites) does NOT have undulatory extinction because it was not strained

One crystal in the grain

http://people.uncw.edu/dockal/gly312/sandstonepet/sandstone.htm

Two or more crystals in the grain

http://en.wikipedia.org/wiki/Undulose_extinction

Chert: many tiny “cryptocrystals” in the grain

Chert grain - The subangular grain on the left is a chert fragment. Internally it is made up of a mosaic of very small crystals ('cryptocrystalline') of quartz. As you rotate this grain under polarized lights, there is a shimmering or flickering effect as each subgrain of quartz goes in and out of extinction

Blue filter light shining through gaps with no cement

Low cement SS are often very friable

Here the cement completely fills gaps between grains

Chalcedony: microcrystalline Quartz

http://faculty.gg.uwyo.edu/heller/Sed%20Strat%20Class/SedStratL1/slideshow_1_14.htm

Quartz Overgrowths- In this quartzite the individual quartz grains are cemented together with a quartz (silicate) cement. Note that cement that precipitated onto a quartz grain grew in 'optical continuity' with its substrate. For example, the right quartz grain with the 'q' label seems to be a big white blob. However, there is a faint dark line that outlines where the original, rounded, grain boundary is. The outer most part of this grain is composed of quartz overgrowth that is also white in this photo. If you rotated this slide under polarized light you'd see that the entire grain, the ghost and its overgrowth, go extinct together.

http://faculty.gg.uwyo.edu/heller/Sed%20Strat%20Class/SedStratL1/slideshow_1_16.htm

Two phases of cementation - This is a quartz sandstone, seen under plain light. The quartz grains have quartz overgrowths (labeled 'o'), reflecting a first phase of cementation, and then, later, a period of carbonate cementation (c) seen as a brownish material filling the pore space.

Calcite cemented sandstone (specifically, a quartz arenite). Well-rounded quartz grains (Q) have euhedral quartz overgrowths beyond their original grain edges (arrows). Calcite (C) has filled remaining pore space.

http://www.gly.uga.edu/speleoatlas/SAimage0223.html

Note very high interference color of the Calcite.

http://faculty.gg.uwyo.edu/heller/Sed%20Strat%20Class/SedStratL1/slideshow_1_17.htm

Calcite corrosion of Quartz - The light yellowish blue colored material here is calcite cement. The black and speckled black blobs are quartz grains. The edges of the quartz grains are corroded and filled in with the calcite cement. Note that calcite tends to precipitate under high pH conditions, but that quartz tends to dissolved under these conditions. So with high pH conditions this type of erosion of the quartz grains with cementation of calcite can occur.

Volcanic lithic grain (Lv) - This grain, seen under plain light, is nicely rounded and internally you can see many, euhedral (i.e. with sharp angular crystal faces) microphenocrysts of plagioclase (note the twinning on these euhedral grains). This is a classic Lv grain, probably from a volcanic arc.

http://faculty.gg.uwyo.edu/heller/Sed%20Strat%20Class/SedStratL1/slideshow_1_9.htm

R = rock fragments

Folk Classification

Embayed plagioclase and calcite cement - The plagioclase feldspars here (note twinning) do not have the nice perfectly round, smooth shape that they probably had originally. Instead the grains have been 'embayed' (partially dissolved away) and calcite cement (bright bluish mosaic) has filled in the embayment. This happens under high pH conditions, where calcite is precipitated and silicates are dissolved. Imagine there were high pH conditions (leading to dissolving the feldspar grains) but no carbonate rich ground water around (so no cement). You can see how this would develop porosity in the sandstone while it was buried underground. Such 'secondary porosity' can be abundant and makes those seeking hydrocarbons quite excited.

http://faculty.gg.uwyo.edu/heller/Sed%20Strat%20Class/SedStratL1/slideshow_1_7.htm

Litharenites are sandstones with a significant (>5%) component of lithic fragments, symbol R or RF.Lithic sandstones are usually associated with one specific type of lithic fragment (i.e., igneous, sedimentary, or metamorphic).

Lithic sandstones form in a wide variety sedimentary depositional associated with active margins. This tectonic setting provides the source of the lithic fragments, either through arc volcanism, thin-skinned faulting, or continental collisions.

This can also occur when minerals are part of a sedimentary rock.

Resolves FeResolves Fe++++ content content

Magnesium Calcite

Coarse carbonate grains called Allochems