SandstoneSandstoneClassificationClassification

Sandstone ClassificationSandstone Classification More than 50 sandstone classificationMore than 50 sandstone classification

systems.systems. Laboratory analysis is required with pointLaboratory analysis is required with point

counting, typically of 500 points, ofcounting, typically of 500 points, ofpetrographic thin sections.petrographic thin sections.

The classification schema that we useThe classification schema that we usehere was first proposed by P.D> krynine inhere was first proposed by P.D> krynine inthe 1940the 1940’’s and F.J. Pettijohn in the 1950s and F.J. Pettijohn in the 1950””ssand 1960and 1960’’s.s.

It was later modified by R.H. Dott, Jr. inIt was later modified by R.H. Dott, Jr. in1964.1964.

Sandstone ClassificationSandstone Classification It can be used for unconsolidatedIt can be used for unconsolidated

modern sand and ancientmodern sand and ancientsandstone.sandstone.

Two percentage are used toTwo percentage are used tosubdivide terrigeneous sandstone:subdivide terrigeneous sandstone: Percentage of matrix- any clasticPercentage of matrix- any clastic

material finer than 30 microns (coarsematerial finer than 30 microns (coarsesilt). Other material such as cement issilt). Other material such as cement isirrelevant.irrelevant.

Composition of sand frameworkComposition of sand frameworkgrains, quartz, feldspar, and rockgrains, quartz, feldspar, and rockfragments (lithics).fragments (lithics).

Sandstone ClassificationSandstone Classification ArenitesArenites- up to 15% of matrix- up to 15% of matrix

content.content. Arenites are texturally clean, matrixArenites are texturally clean, matrix

free or matrix poorfree or matrix poorsandstone.Cohesiveness is due tosandstone.Cohesiveness is due tocement precipitates in what wherecement precipitates in what whereoriginally empty intergranular pores.originally empty intergranular pores.

WackesWackes (or graywackes)- 15% - (or graywackes)- 15% -75% of matrix content.75% of matrix content.

Wackes are argillaceous, matrix-Wackes are argillaceous, matrix-rich, texturally immature, or rich, texturally immature, or ““dirtydirty””sandstones.sandstones.

Sandstone ClassificationSandstone Classification

Matrix originates in two principal ways.Matrix originates in two principal ways. Primary detrital matrix is transported andPrimary detrital matrix is transported and

deposited with the coarser sand-sizedeposited with the coarser sand-sizeframework grains.framework grains.

Secondary matrix is produced by diagenesis:Secondary matrix is produced by diagenesis:rock fragments are squashed androck fragments are squashed anddisaggregated, and feldspar decomposes todisaggregated, and feldspar decomposes toform clay. The origin of this matrix must beform clay. The origin of this matrix must beinferred to understand the sandstoneinferred to understand the sandstonecontaining it.containing it.

Sandstone ClassificationSandstone Classification

The percentage ofThe percentage ofquartzquartz, , feldspafeldsparr and androck fragmentsrock fragments allow the allow thearenites and wackes toarenites and wackes tobe further subdivided.be further subdivided.Other frameworksOther frameworksconstituents such asconstituents such asmicas and heavymicas and heavyminerals are ignored.minerals are ignored.

Quartz arenites and quartzQuartz arenites and quartzwackes: Sandstones withwackes: Sandstones withframework grainsframework grainscomposition mainly of quartzcomposition mainly of quartz(95% or more).(95% or more).

Lithic- The prefix lithic isLithic- The prefix lithic isused for arenites andused for arenites andwackes in which rockwackes in which rockfragment s exceedsfragment s exceedsfeldspar.feldspar.

When feldspar exceed rockWhen feldspar exceed rockframework are calledframework are calledfedspathic or arkosic.fedspathic or arkosic.

Ratio of Quartz to feldsparRatio of Quartz to feldsparand Rock Fragmentsand Rock Fragments

This ratio is an index of compositionalThis ratio is an index of compositionalmaturity, reflecting the difference betweenmaturity, reflecting the difference betweensand with lots of soft, unstable,sand with lots of soft, unstable,decomposable rock fragments anddecomposable rock fragments andfeldspar. Weathering and recycling shouldfeldspar. Weathering and recycling shouldultimately generate sand residuesultimately generate sand residuescomposed of only the most resistantcomposed of only the most resistantmaterials.materials.

Quartz arenitesQuartz arenites Typically white to light gray but can beTypically white to light gray but can be

stained pink, brown, or red by iron oxidestained pink, brown, or red by iron oxidecement.cement.

Consist almost entirely of sand-sizedConsist almost entirely of sand-sizedmonocrystaline quartz grains. Resistantmonocrystaline quartz grains. Resistantgrains of chert, metaquartzite, and heavygrains of chert, metaquartzite, and heavyminerals such as tourmaline, zircon, andminerals such as tourmaline, zircon, andrutile also can be present.rutile also can be present.

Chemical composition of 95% - 97% SiOChemical composition of 95% - 97% SiO22,,0.5% - 1.0% Al0.5% - 1.0% Al22)O)O33 (detrital feldspar), and (detrital feldspar), and1.0% CaO and Co1.0% CaO and Co22..

Supermature texture and composition.Supermature texture and composition.