Sedimentary Rock - Chapter 4 Classification

8/13/2019 Sedimentary Rock - Chapter 4 Classification

1/46

1/8/2014 Geology 3153 Part 4. 1

Part 4. Sedimentary Rock Classification.

4A. Introduction.

4B. Clastic Sedimentary Rock Classification.1. Conglomerates and Breccias.2. Sandstones.3. Mudrocks.

4C. Carbonate Rock Classification.

4D. Other Sedimentary Rocks.1. Organic Carbon-Rich Sedimentary Rocks.2. Iron-Rich Sedimentary Rocks.3. Siliceous Sedimentary Rocks.4. Phosphates.

5. Evaporites.


2/46

1/8/2014 Geology 3153 Part 4. 2


4A. Introduction.



4D. Other Sedimentary Rocks.1. Organic Carbon-Rich Sedimentary Rocks.2. Iron-Rich Sedimentary Rocks.3. Siliceous Sedimentary Rocks.4. Phosphates.5. Evaporites.


3/46

1/8/2014 Geology 3153 Part 4. 3


4A. Introduction.

To this point, we have been discussing the constituent particles andthe origin of the particles that make up sediments and sedimentaryrocks.

Our attention now turns to the classification of sedimentary rocks.

Although many classification schemes have been proposed and aretaught at other institutions, the schemes presented herein arearguable the most widely used and/or most useful for mostapplied geology endeavors.

Why do scientist like to make classifications? What is the purpose of

classification?


4/46

1/8/2014 Geology 3153 Part 4. 4


4A. Introduction.

Why do scientist like to make classifications? What is the purpose ofclassification?

Classification is the process of defining systematic order tovarious phenomena.

In science, it is an attempt to organize natural phenomena.

Classification schemes can be

strictly descriptive, or

explicitly or implicitly genetic (i.e. the organization isaccording to the understood origin of a phenomena).

A problem with classifications that have a strong genetic aspectis that they are only as valid, useful as our understanding of theorigin of the phenomena being classified.


5/46

1/8/2014 Geology 3153 Part 4. 5


4A. Introduction.

Why do scientist like to make classifications? What is the purpose ofclassification?

A name communicating an ideais the most useful outcome of anyclassification scheme.

3 rock attributes used in classification:

texture = the size and shape of the constituent particles;composition = the type (mineral, mineralloid, etc.) of the particles;fabric = spatial arrangement of the particles.

In classifying sedimentary rocks, fabric is mainly used to distinguishbetween:

sediment = unconsolidated sedimentary particles, androck = consolidated sedimentary particles

(by compaction and/or cementation).


6/46

1/8/2014 Geology 3153 Part 4. 6


4A. Introduction.

General classification sedimentary rocks is based on ourunderstanding of the origin of the constituent particles:

clastic = broken particles derived from weathering ofpre-existing rock, and transported to siteof deposition

biochemical= particles resulting from biologicallymediated chemical precipitation, and areformed in or near site of deposition

chemical = crystalline particles resulting from directchemical precipitation from an aqueoussolution, and are formed in or near site ofdeposition


7/46

1/8/2014 Geology 3153 Part 4. 7


4A. Introduction.

Volumetric proportion in Earths sedimentary shell:

Rock and Estimatedsediment equivalent volume

conglomerates 1-2 %sandstones 10-20 %mudrocks 50-80 %carbonates 10 %others ~5 %


8/46

1/8/2014 Geology 3153 Part 4. 8


4A. Introduction.



4D. Other Sedimentary Rocks.1. Organic Carbon-Rich Sedimentary Rocks.2. Iron-Rich Sedimentary Rocks.3. Siliceous Sedimentary Rocks.4. Phosphates.5. Evaporites.


9/46

1/8/2014 Geology 3153 Part 4. 9


4B. Clastic Sedimentary Rock Classification.

Clastic sedimentary rocks are classified by either an emphasis on textureor composition.

As we discussed in Part 3, clastic sedimentary particles can communicateinformation about:

character or depositional processes and history of abrasion ~texture;

type and degree of pre-existing rock weathering ~composition.


10/46

1/8/2014 Geology 3153 Part 4. 10



Primary subdivision of clastic sediments and sedimentary rocks isbased on texture:

Gravel Sand:Mud Sediment RockPercentage Ratio

>30% not used Gravel Conglomerate(subangular or better roundness)

Rubble Breccia(angular or poorer roundness)

1:1 Sand Sandstone


11/46

1/8/2014 Geology 3153 Part 4. 11



4B.1 Conglomerates and Breccias.

Because of their coarser texture, conglomerates and breccias aredominated by rock fragments. Thus, classification emphasizestexture.

Wentworth grain size class names are used based on median size ofthe framework grains, for example:

cobble gravel = 256 to 64 mm clastic sediment;cobble conglomerate = 256 to 64 mm clastic rock.

Roundness is already utilized in name (see previous slide).


12/46

1/8/2014 Geology 3153 Part 4. 12


4B. Clastic Sedimentary Rock Classification.4B.1 Conglomerates and Breccias.

Because most gravels and conglomerates are moderately sorted,sorting modifiers are only used for extreme cases, for example:

very poorly sorted boulder breccia;well sorted granule conglomerate.

Compositional aspects can be introduced by using the terms:

monomicticmeaning >75% of a single rock fragmentfor example, monomictic quartzite granule conglomerate

polymicticreferring to a mixture of rock fragment typescan include in name dominate rock fragment type

In general, but not always (consider texture too), monomicticindicates proximity to source. Why?


13/46

1/8/2014 Geology 3153 Part 4. 13


4B. Clastic Sedimentary Rock Classification.4B.1 Conglomerates and Breccias.

To assist in writing of rock names, a general form can be used.

General form for conglomerates and breccias:

composition modifier | texture modifier | root name

root name: gravel, rubble, conglomerate or breccia

texture modifier: Wentworth gravel class name;where appropriate use roundness (if extremecase) then sorting modifiers

composition modifier: dominate rock fragment typed; monomictic orpolymictic

Recall from English grammar the organization of modifiers foremphasis and logical association; compound punctuation debatable.


14/46

1/8/2014 Geology 3153 Part 4. 14



4B.2 Sandstones.

Naming of sandstones depends on emphasis:

texture if emphasis is sedimentary process, or

composition if emphasis is source rock.

In other words, consider what it is you are attempting tocommunicate to others. What is emphasis, purpose of your study?


15/46

1/8/2014 Geology 3153 Part 4. 15


4B. Clastic Sedimentary Rock Classification.4B.2 Sandstones.

Texture emphasis:

general form of a name:

composition modifier | texture modifiers | root name

root name: Wentworth size class for median size

texture modifiers:first (right) is sortingsecond (left) is roundness

composition modifier: see below; use ic suffix; can be optional

example: quartz arenitic, well rounded, well sorted fine sandstone


16/46

1/8/2014 Geology 3153 Part 4. 16



Composition emphasis:

The most widely used sandstone compositional root names comefrom the Folk Classification.

ternary diagram poles:Q = quartz + quartziteF = feldspars + plutonic and

gneiss rock fragmentsR = all other rock fragments

specific names for litharenites:Volcanic LithareniteSedimentary LitharenitePhyllarenite = meta-lithics


17/46

1/8/2014 Geology 3153 Part 4. 17




Rationale behind QFR poles:

Q = likely first-cycle if >75% Q grains subrounded or poorer;

possible recycle if >95% Q grains well rounded or better;definite recycle if abraded quartz overgrowths present

F = first cycle plutonic or gneiss

R = first cycle if R grains are metamorphic or volcanic;

recycle if R grains sedimentary

A name communicating a much broader idea or implication.


18/46

1/8/2014 Geology 3153 Part 4. 18




general form of a name:

texture modifiers | root name

root name: use Folk composition name

texture modifiers:first (right) is Wentworth size class namemiddle is sorting

third (left) is roundness


19/46

1/8/2014 Geology 3153 Part 4. 19




examples (consider framework composition only):

Q=96% F=2% R=2% is a Quartz Arenite

Q=62% F= 30% R=8%(meta) is a Arkose

Q=52% F=30% R=8% Biotite=10% is a ???

need to recalculate QFR to 100%

Q=58% F=33% R=9% is an Arkoseor biotite-bearing Arkose


20/46

1/8/2014 Geology 3153 Part 4. 20



4B.3 Mudrocks.

Recall that mud is the sediment grain size category for sizes


21/46

1/8/2014 Geology 3153 Part 4. 21


4B. Clastic Sedimentary Rock Classification.4B.3 Mudrocks.

Mudrock classification is based on texture and degree of fissility:

fissility = tendency to break parallel to bedding planes.

very uncommon

most common

common

Mud Sediment RockFraction Nonfissile Fissile

>2/3 silt silt siltstone silt shale

silt ~ clay mud mudstone mud shale

>2/3 clay clay claystone clay shale


22/46

1/8/2014 Geology 3153 Part 4. 22


4B. Clastic Sedimentary Rock Classification.4B.3 Mudrocks.

General form of a name:

color | compositional modifier | root name

root name: use sediment or rock texture name

composition name: use mineral or other constituents

color: good indicator or oxidation state

examples:

red kaolinite claystone;brown smectite mud shale;black carbonaneous clay shale


23/46

1/8/2014 Geology 3153 Part 4. 23


4A. Introduction.




5. Evaporites.


24/46

1/8/2014 Geology 3153 Part 4. 24



What is the general occurrence of carbonates and clastics?

Sediments or rocks that contain >50% carbonate frameworkgrains and matrix is a carbonate.

As a general rule, carbonates contain can contain some sand and

gravel, but contain very little or no mud. However, carbonate andmuddy clastics do occur interlayered with each other.

think about

wherecarbonatesoccurtoday

sand

and

gravelmud

carbonate

sediment

segregation by

biological tolerance

segregation by

transpor t mode

stipple area denotes

most common occurrence


25/46

1/8/2014 Geology 3153 Part 4. 25



Like clastic rock classifications, carbonate rock classificationsconsider both the rock texture and composition.

Unlike clastics, carbonate rock classifications do not consider thedetails of the textural attributes because they are not, bythemselves, particularly significant

carbonate grains come in wide variety of sizes, shapes andbulk densities.

What is significant:

1) proportion of carbonate framework grains to matrix, whichis ubiquitous in carbonate sedimentary environments;

2) carbonate grains that are not organically bound (e.g. looseskeletals, peloids, etc.); and

3) carbonate structures formed by organic bounding.


26/46

1/8/2014 Geology 3153 Part 4. 26



If the original depositional fabric is recognizable, then use

Embry-Klovan Classification, where is here modified as adecision tree (Kerr, unpublished).

Other carbonate classification schemes are available, but these

either require microscopic analysis or are overly simplistic.

The Embry-Klovan classification is being used widely in moderncarbonate literature.

This classification is an elaboration of the older Dunham

Classification for carbonate rocks.


27/46

1/8/2014 Geology 3153 Part 4. 27



If the original depositional fabric is not recognizable, then use

crystalline limestone= dominated by calcite

crystalline dolostone= dominate by dolomite

in the recent literature, it is preferable to make the distinctionbetween:

dolomite = mineral, anddolostone = rock dominated by mineral dolomite

the prefix dolo- can be used with Embry-Klovan names too;for example, dolograinstone


28/46

1/8/2014 Geology 3153 Part 4. 28



Modified Emery-Klovan Classification.

The original illustration for theclassification had a series ofhierarchical boxes that eventuallylead to a carbonate name.

My attempts to teach, explainthis illustration kept leading tothe asking of a series of questionsthat lead to a name in other words,following a decision tree.

Admittedly, such names may seemalien to you. Just keep in mind thatthe names should conjure up an imagethat we will relate to carbonateenvironments later in the semester.


29/46

1/8/2014 Geology 3153 Part 4. 29



Unfortunately, the mudstone is found in both clastic and carbonateclassifications. If you are dealing with both, then you should make aclear distinction, for example:

clastic mudstone, or carbonate mudstone.

In determining if a carbonate rock is framework-supported use thefollowing guide:

for equants, it is frame-support if >60% grains;

for non-equants, it is frame-support down to 45% grains.


30/46

1/8/2014 Geology 3153 Part 4. 30



Many organisms, both past and present, are found or form rigid orsemirigid frames (i.e. organically bound).

Such organisms are generally referred to as framebuilders.

Bounding is by:

buidling a rigid frame; for example, corals, bryozoans & sponges;

encrustingor bindingsediment; for example, red algae andcyanobacterial mats;

acting as bafflesto slow currents promoting sedimentdeposition; for example, phylloid algae

The type of fossil organisms and consequence organic boundingmechanism is dependent on geologic age. Why?


31/46

1/8/2014 Geology 3153 Part 4. 31



mainly

Bafflestonesand

Bindstones

mainly

Framestones

d k l f


32/46

1/8/2014 Geology 3153 Part 4. 32



General form of a name:

modifier | root name

root name: use Embry-Klovan, or crystalline designation

modifier: list major grain types or framebuilders with most near root

examples:

P 4 d R k Cl f


33/46

1/8/2014 Geology 3153 Part 4. 33



examples:

1) 5% pebble-size and 70% sand-size coral fragments;20% micrite; 5% porosity:

Note: the usual routine is to make your own observations;

here we will have to use certain key words to guide yourdetermination of an appropriate rock name.

fragments = broken, transported particles

coral packstone

P 4 S di R k Cl ifi i


34/46

1/8/2014 Geology 3153 Part 4. 34



examples:

2) 30% rudist clams in growth position; 20% calcite cement50% porosity:

in growth position and in life position = if

framebuidlers, then clue for organic bounding

rudist framestone

phylloid algal isanother keyword

for organicbaffle actor

P 4 S di R k Cl ifi i


35/46

1/8/2014 Geology 3153 Part 4. 35



examples:

3) 10% peloids; 20% sand-size skeletals; 70% micrite:

peloid, skeletal wackestone

P t 4 S di t R k Cl ifi ti


36/46

1/8/2014 Geology 3153 Part 4. 36



examples:

4) 20% gravel-size intraclasts; 60% skeletal fragments;10% micrite; 10% porosity:

intraclast, skeletal rudstone



37/46

1/8/2014 Geology 3153 Part 4. 37


4A. Introduction.




5. Evaporites.



38/46

1/8/2014 Geology 3153 Part 4. 38


4A. Introduction.

4A.1. Organic Carbon-Rich Sedimentary Rocks.

Organic carbon in sediments and rocks is largely controlled bypreservation conditions:

reducing chemical conditions ( Eh ); and

removal from degradation by aerobic and anaerobic bacteria.

Places:

lakes with seasonal ice cover or stagnation;

silled basins with isolated bottom waters;

continental slope below upwelling circulation.



39/46

1/8/2014 Geology 3153 Part 4. 39


4A. Introduction.

4A.2. Iron-Rich Sedimentary Rocks.

Where iron is of sufficient concentration and transportationconditions favorable, iron-rich sedimentary rocks are mined for ironore.

A variety of minerals see notes.

Occurrences and origins:

Phanerozoic oxisol soils and paleosols;

large influx of Fe+2(highly mobile) in to oxygen-rich waters;

Archean-Proterozoic Banded Iron Formation related toevolutionary introduction of algae and other photosynthesizers.

P t 4 S dim t R k Cl ssifi ti


40/46

1/8/2014 Geology 3153 Part 4. 40


4A. Introduction.

4A.2. Iron-Rich Sedimentary Rocks.

Banded IronFormation:

http://www2.bc.edu/~strother/GE_146/lectures/pics21/bif.html

P rt 4 S dim nt r R ck Cl ssific ti n


41/46

1/8/2014 Geology 3153 Part 4. 41


4A. Introduction.

4A.3. Siliceous Sedimentary Rocks.Chert is a non-clastic sedimentary rock made up of microcrystallinequartz, which is also know as chalcedony.

The original source of silica comes from microscopic animal and plant

skeletal material.

Transformation with burial:

silica oozeopal/christobalite gelchalcedony rock

Can occur as chert beds, and as chert nodules in carbonates andclastics, particularly mudrocks.

Part 4 Sedimentary Rock Classification


42/46

1/8/2014 Geology 3153 Part 4. 42


4A. Introduction.

4A.4. Phosphates.The most economically available occurrence of phosphate is insedimentary rocks. The most common mineral is apatite, a calciumphosphate.

Modes of occurrence:

ooids and peloids;selective early replacement of skeletal debris;nonselective replacement, usually as nodules, of matrix.

Places of occurrence:

under upwelling circulation (rising phosphorous-rich deep water;far offshore away from dilution effects of clastics and carbonatesediment accumulation.



43/46

1/8/2014 Geology 3153 Part 4. 43


4A. Introduction.

4A.5. Evaporites.Evaporite sedimentary rocks are examples of chemical sedimentaryrocks, that is the result of direct chemical precipitation from aqueoussolution.

Most evaporite accumulations are associated with concentrations ofseawater through evaporation (arid climate).

Top 5 Dissolved SubstancesFresh Water Sea WaterTDS = 0.01% TDS = 3.5%

HCO3-and CO3-2 Cl-Ca+2 Na+

H4SiO4 SO4-2

SO4-2 Mg+2

Cl- Ca+2



44/46

1/8/2014 Geology 3153 Part 4. 44


4A. Introduction.4A.5. Evaporites.

Modes of occurrence:

bedded evaporites crystallization in water column settling tobottom and crystallization

nodules in carbonate mud crystallization from pore waters

gypsum (anhydrite) nodules commonly display fabrics:

enterolithic (intestine like) merging of nodules; andchicken wiresegregation of impurities



45/46

1/8/2014 Geology 3153 Part 4. 45



The origin of thick accumulations of evaporite minerals was firstelucidated by Usiglio, Italian chemist mid-1850s, who observed theorder of mineral precipitation by evaporating Mediterranean seawater:

1,000 m tall column of seawater yields 14.9 m thick deposit

mineral order:

first calcite/aragonitedolomitegypsum/anhydritehalite

last potassium salts



46/46

1/8/2014 Geology 3153 Part 4. 46



How well does Usiglios experiments compare to natural occurrence ofevaporite deposits?

Evaporite deposits are typically 1,000s meters thick; by experimentthis would require a single column of seawater 67,340 meters tall

(c.f. abyssal ocean depths only 3,000 m).

In nature, evaporite mineral successions are incomplete or repeated.

Was Usiglios experiment wrong? No, difference between closed(test-tube) systems and open systems.

natural systems replenished with seawater and isolated basins

Arid lake deposits typically include borate minerals.

Documents

Sedimentary Rock - Chapter 4 Classification