THE ORIGIN OF - PowerPoint Presentation

Slide1

THE ORIGIN OF CLAYS

But why clay-

It is important to know where we are coming from , since the course of study in MNA/IMACS centers on clay and clay minerals basicallySlide2

How are clays formed

Clays are formed from weathering of silica rich rocks

e.g

Granite

Processes of Formation-

-Weathering of the silica rich rock

-bedrock weathering

-transporting of the weathered rocks

-Sedimentary processes

-Incorporation of CarbonatesSlide3

Requirements

-

ReactionTime

- Igneous Rocks (Intrusive Igneous Rocks)

-Geological Factor

-Agents of Transportation

Agents of Weathering

-Alteration of Chemical composition

-Pressure

-TemperatureSlide4

Types of Clays –Based on Origin

1-Residual Clays-not far from parent rock

2-Sedimentary Clays -far from parent material

Residual Clay (primary clays)–Non

plastic,white,e.g

kaolin

Sedimentary Clay (secondary clays)-

Plastic,grey,darker,smaller

paricles

and uniform

e.g

ball

clay,fire

claySlide5

Residual clays are formed basically by surface weathering

This gives clays in 3 ways

-chemical decomposition of rocks

-solution of rocks(limestone)containing clayey impurities which are insoluble

-

disintergration

and solution of

shales

But the most common process of clay formation is the

decompostion

of feldsparSlide6

SOME INTRUSIVE ROCKS

Coarse Grains-slow cooling

Clays are not formed from Extrusive rocksSlide7

DioriteSlide8

GraniteSlide9

Granite pegmatiteSlide10

GabbroSlide11

Mechanisms of clay minerals formation

-Inheritance

-

Neoformation

-Transformation

The 3 mechanisms operating in 3 geological systems

-Weathering

-Sedimentary

-

Diagenetic

hydrothermalSlide12

Inheritance

Another area reaction

Stable

Natural deposit

Previous stage in rock cycle reaction

Dominace

in sedimentary environmentsSlide13

Neoformation

Clays precipitation from solution

Reaction of amorphous materialSlide14

Neoformation

Secondary precipitates of calcite ,

sulphates

, Fe

Affirmation of permafrost

Structural and mineralogical changes are irreversible and affect present soils

Understanding of

quartenary

environment-needs assessment of possible frozen groundSlide15

Transformation

Possesion

of inherited structure

Chemical reactions-ions exchanged and modification of

cations

(layer transformation)

1)ion exchange between

losely

bound ion and those of environments

2)layer transformation –modification of arrangement of octahedral, tetrahedral and interlayer

cations

Dominance in

diagenetic

-hydrothermal environmentsSlide16

The best mechanism

Layer transformation

Result of this type of reaction are better preserved in geological recordsSlide17

Environment of formation

1)Weathering zone

Upper zone of the earth crust –T and P varies

Short reaction time

2)Sedimentary environment-long reaction time(

sedimentation,subsidence

)

-near or below sea level

Sediment-water interface

-low temperature

Pressure (1 kb )Slide18

Diagenetic

hydrothermal

-zones in contact with hot water

-wide range of environmental conditionsSlide19

Incresing energy required

Mechnism

/

environments

inheritance

neoformation

transformation

sedimentary

weathering

Diagenesis

-hydrothermalSlide20

CONTROVERSIAL ISSUE OF DETRITAL VS DIAGENESIS

ORIGIN OF CLAYS

DETRITAL OR DIAGENESISSlide21

Detrital

-reflection of character of source material, inheritance of basic clay mineral lattice

Diagenesis

-adsorption of

cation

and its modificationSlide22

Application of XRD in Detrital

vs

Diagenesis

controversy

-Collection of thousands of samples

-to illustrate the variety of clay under similar environmental conditions

-variety of environments in which same clay minerals occurSlide23

XRD OF ORGANIC AND PYRITE RICH SHALES

-No particular clay mineral is restricted to a particular environments

-dominance of

kaolinite

in

fluviate

environment

-

illite

,

monmorillionite

abundance,frequency,sole

clay mineral in all environments

-

chlorite

not a dominant mineral

-non marine

shales

are

seldom,if

ever

monomineralicSlide24
Slide25
Slide26
Slide27
Slide28

interpretation

-clay minerals do not originate from depositional environments

-they are

detrital

in origin

-though they are altered(degraded) in

fluviate

and

subaerial

environments

But little evidence of alteration in major basin of deposition to show that it is a major factor in defining the ultimate

mineralogic

character of clay Slide29

TYPES OF CLAYS BASED ON GROUPS

-KAOLINITE

-MONTMORILLIONITE

-SMECTITE

-ILLITE

-CHLORITESlide30

BASED ON GENERAL COMPOSITION AND PROPERTIES

-KAOLIN-consist mainly of

kaolinite

-BENTONITE-majorly

monmorillionite,hardens

when mixed with water

-BALL CLAY-

kaolinite

, mica

-FIRE CLAY-

kaolinite

,

feoxide,magnesia,alkalines,can

resist high temp

-COMMON CLAY-no resistance to heat, has impurities than fire clay

-ARMENIAN BOLE-

attapulgiteSlide31

Bibliography

Clay mineral formation and transformation in rocks and soils by D.D EBERL , US Geological survey

A discussion on the origin of clay minerals in sedimentary rocks by Charles .E Weaver, Shell Oil

Co,Houston,Texas

Identification of Clay minerals by

Xray

Diffraction Analysis by George W

Brindley

The origin of clay minerals in

soilsand

weathered rocks,

www.springer.com

Clay types, geologic origins by ARTS

186 DirectorySlide32

NOW THAT WE KNOW WHERE WE ARE COMING FROM , WE CAN IDENTIFY WHERE WE ARE GOING TOSlide33

THANKS FOR LISTENING

MERCI POUR VOTRE ATTENTION