basic concepts underlying the science of geology

7/23/2019 Basic Concepts Underlying the Science of Geology

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SOME BASIC CONCEPTS UNDERLYING THE SCIENCE OF

GEOLOGY

GEOLOGY - THE SCIENCE OF THE SOLID EARTH AND ITS INTERNAL

PROCESSES, INFLUENCED ALSO BY THE ATMOSPHERE,

OCEANS/RIVERS, AND BIOLOGICAL ACTIVITIES - COMES FROM THEGREEK WORDS GEOS (EARTH) AND LOGOS (STUDY). PLANETOLOGY

INVOLVES ON-SITE AND SENSOR INVESTIGATIONS OF THE OTHER

SOLAR (AND NOW EXTRASOLAR) PLANETARY BODIES, USING MAINLY

COMPARISONS TO TERRESTRIAL GEOLOGICAL FEATURES AND

PROCESSES AND APPLYING METHODS OF ANALYSIS PROVEN

EFFECTIVE FOR EARTH STUDIES.

Th S!" F#$%&'$& C*$+ &*# h E&h0 G**12

1. The Earth formed about 4.6 billion years ago, along with the other solar planets and the Sun itself. The planets built up by accretion of rocky and gaseousdebris (asteroidal, planetesimal meteoritic! materials and comets" throughcollision of orbiting bodies. #ided by gra$itational attraction which helped tocompact these material, early on the assembling Earth underwent partial tocomplete melting, separation of different materials into an inner and outer core(%ron&'ickel", an etensi$e interior mantle, (%ron)*agnesium)+alcium&richsilicates", and a thin crust (enriched in Silica, Sodium)otassium)#luminum", all(ecept the outer core" solidifying by cooling o$er the first few hundred millionyears- escaping gases produced an atmosphere (principaly , +/0, ', +4" were

held abo$e the solid Earth by gra$ity owing to its large mass- in time (about 4billion years ago", the Earths eterior cooled sufficiently to allow $ast $olumes of water $apor to condense, forming in lower areas great concentrations of water collected into depressions (oceanic basins".

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0. The Earths materials are di$erse and $ariable. *ost $ariation occurs in theoutermost 022 kilometers, in the lithosphere. Igneous rocks form directly bycrystalli3ation of hot melts made up of silicates (Si m/n" combined with e, *g,+a, #l, 'a, 5, Ti, 0/". *inerals formed from these make up nearly all the mantleand crust. ocks at the surface decompose)disintegrate by reaction with theatmosphere)hydrosphere to produce solid debris and soluble chemicals that aretransported)deposited to form sediments, that upon burial are con$erted toSedimentary rocks (usually layered- strata". re$iously formed rocks that areheated and pressuri3ed when buried to shallow to moderate depths (7 to 82 km"of the crust recrystalli3e as solids under increased temperatures and pressures

to form Metamorphic rocks (some may melt". The abo$e processes comprisethe Rock Cycle, shown below, and discussed in more detail on this page.

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These rocks are usually distincti$e in the field (out&of&doors". %gneous rocks aremade from crystals & minerals that crystali3ed from once hot melts. %ntrusi$eigneous rocks are commonly without notable layering & they can be described asmassi$e, and result from cooling and solidification well beneath the Earthssurface. 9ranite is the most familiar intrusi$e rock type. Etrusi$e igneous rocksoften occur in layers, which may $ary in thickness, formed either by outflows of la$a or accumulation of debris tossed into the air by erupting $olcanoes. :asalt is

the pre$alent etrusi$e rock. ield eamples of each are;

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Sedimentary rocks are nearly always in layers. These are beds (also calledstrata" made up of deposits from the ocean or other water bodies that consist of clastic fragments (e.g., sand grains", or chemical or biochemical precipitates.*ost fre<uently, the layers are initially laid down as hori3ontal units. The mostcommon types of sedimentary rocks are shales, mudstones, sandstones,

limestones, and e$aporites (such as salt beds". %f the strata are inclined (dipping",this usually means that the rocks ha$e subse<uently been pushed by mountain&building forces that ha$e tilted or folded the units. ere are eamples;

Shales are the most common sedimentary rock type, being made up of fineparticles (mud is composed of such small particles". Shales are usuallycharacteri3ed by their tendency to break along thin layers called parting.

*udstones lack this feature. ere is a typical outcrop of shale beds;

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Sandstones are made up of sand&si3ed grains. *ost common is <uart3, theprincipal constituent of the thick sandstone beds seen below (graywackes arecomposed of sand fragments of eroded basaltic rocks- arkoses consist of fragments from granitic rocks"

=imestones are the principal member of carbonate rocks. Typically, the limestoneis a light whitish&gray, as seen in this outcrop;

The bedding of sedimentary rocks is often conspicuous e$en when $iewed fromspace, as shown by these limestone and sandstone units in 'amibia.

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*etamorphic rocks result from the action of heat and pressure on pre&eistingrocks (usually sedimentary" that are brought to depths of a few to tens of kilometers below the surface. 'ew minerals are produced by this metamorphism.Shales (mudstones" may be recrystalli3ed into mica&rich rocks called schists. #ssuch rocks are heated to temperatures below but not far from those that wouldmelt the rocks, they become soft, recrystalli3e further, and can be deformed intocrenulated light and dark units that resemble layers, forming rocks calledgneisses. Eamples of slate, schist and gneiss are;

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>. The Earths outer shells (crust and upper mantle ? lithosphere", about 172&022kilometers thick under the continents (less so under the oceans", are sub@ected todynamic forces that cause segments of the shells and materials at the top, tobreak up into plates and deposits on them that mo$e laterally, bringing aboutdeformation of their constituent rocks (mainly in and on the crust" by bending,folding, flowing, fracturing, mo$ement of blocks along faults, and melting. Thebranch of geology that studies these deformational effects is known as Structural9eology. The dynamic processes, dri$en mainly by heat (much supplied by

radioacti$e element decay" and gra$ity and resultant con$ection within and belowthe lithosphere (in the mantle", mo$e plate units either away from each other or against each other (both situations can affect a plate"- this general motion iscalled plate tectonics. lates di$erge from ridges rising from within oceanicbasins (lower areas underlain by basaltic crust" and con$erge against boundariesof other plates (whose outer rocks are either oceanic or continental in nature andcomposition", causing melting, $olcanism, metamorphism, mountain building,rise)fall of crustal blocks, continental growth and splitting.

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This net illustration has some of the inherent aspects of the plates within it. %tshows howe$er subdi$isions of the continents in terms of structural settings thatinclude 1" Shield (old igneous)metamorphic complees- also called the craton"-0" latform (supracrustal flat&lying sedimentary rocks"- >" /rogen (mountainbelts- deformed rocks"- 4" :asin (regions where sedimentary rocks ha$eaccumulated in geologically more recent times"- 7" =arge %gneous ro$ince(areas of considerable co$er by basaltic rocks"- 6" Etended crust (parts of thecontinental crust now co$ered by marine waters".

The pre$ious two maps show large units of the Earth continental and oceaniccrust. #t much smaller scales, rocks within the plates are sub@ected to pressuresthat cause them to bend or break. This ground photo shows folds and a fault(where rock is broken and displaced".

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The two principal types of bends (folds" appear in this photo & the upward arch(left" is called an anticline and the downward bend is a syncline. olds are theresult of compressi$e stresses (the rocks are ApushedA by eternal forcescausing them to buckle or AwrinkleA".

The geometry of folds gi$es rise to different descripti$e terms that relate to theattitude of the limbs (either side" of the fold with respect to the hori3ontal (theinclination of linear or tabular features such as layers or strata is referred to asAdipA". These are the terms.

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ere is a ground photo of tight (isoclinal" folding. The upfold on the left is ananticline- on the right is a downfold or syncline;

This is a recumbent fold (Alying on its sideA".

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olds tend to die out at either end as one looks down on them. This effect iscalled AplungingA and is illustrated here;

'ote something else in this diagram. There is a general rule, the A=aw of SuperpositionA, that says younger layers of sedimentary rocks are laid downsuccessi$ely on top of older layers below. 'ote the se<uence of strata in thediagram. %n the anticline, the erosional surface (the hori3ontal plane" hasproduced a pattern in which the older rocks are interior to those on either side.The re$erse is true for the syncline so that the younger rocks are interior. Thishold for folds in general.

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ere is an aerial $iew of a plunging anticline in Byoming- below it is the surfaceof folded rocks with pronounced plunging as seen in a satellite image (the patterncan become comple";

#s seen from the air, a circular to elongate anticlinal fold comprises a dome- theolder strata are eposed in the center;

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#t a small scale (outcrop&si3ed", contorted folds are found in metamorphic rockssuch as gneisses. The rocks actually soften (see below" as they are heatedduring deep burial. This type of folding, called ptygmatic, is illustrated here;

aults result from rocks that are stressed (usually resulting in folding" that thenbreak with rocks on either side of the fault plane being displaced (shifted" so asto create a discontinuity. aults are gi$en names that indicate the mode of stressand geometric nature of the displacement. The etensional (when the rock unitsare sub@ect to tension stresses" fault is commonly known as a normal fault , thecompressional type is called a reverse fault if the fault plane is high angle and athrust fault if low angle- the transform fault is one type of wrench or rift faults thatis associated with oceanic ridges.

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# small fault is seen in this ground outcrop. The fault & a plane & appears as a linemarking a discontinuity in the once continuous sedimentary layers. ocks on theleft side are displaced upwards;

:oth a normal fault and a re$erse fault are eposed at this outcrop.

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This fault can be recogni3ed from the air as a line with dissimilar surface features

on either side because the crustal blocks ha$e shifted hori3ontally relati$e toeach other- the mo$ement is mainly hori3ontal making this a strike&slip fault.;

The most famous fault in 'orth #merica is the San #ndreas fault of +alifornia &another strike&slip fault. This reknown photo from the air shows offset of orangegro$e trees as the west side of the fault mo$ed northward.

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# thrust fault usually de$elops when an o$erturned fold breaks. ocks aresho$ed up and outward such that older rocks are carried on top of younger (re$ersing the =aw of Superposition", as shown here;

/n a geologic map rock units are represented by different colors. %n an area inwhich faulting has occurred, the fault trace at the surface is rendered as a blackline- rock units on either side will show abrupt color mismatches;

ocks sub@ected to stress also can break without any displacement. Theseplanar breaks (in effect, fractures" are called joints. ere are three eamples;

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# <uestion may ha$e crossed the readers mind, to which we will now try torespond. ocks when held in the hand or eamined in the field that are struckwith a hammer usually break into chunks, that is, they are brittle. ow then cangreat masses of rocks, particularly those that are layered, bend and fold withoutbreaking into bitsC Se$eral factors make up an answer. These are; confiningpressure, heat, time, slow rate of deformation. #ll but the surficial rocks in$ol$ed

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in mountain&building deformation are buried. #ny indi$idual part of the rockassemblage (imagine a cube of material" is confined by its neighboring rockmasses. The rocks are sub@ected to heat from the Earths interior and other sources. They are pressed upon by eternal forces (see net page". Thepressures are eerted o$er long periods of time. Dnder these conditions rocks

beha$e as though they were AsoftA or ductile rather than brittle. (*etamorphicrocks that contort erratically are actually more like taffy than like hard rock." Theytend to deform at microscopic le$els along atomic slip planes and a macroscopicle$els along bedding planes. Slow deformation that produces folds takes millionsof years as the rocks are gradually displaced. :ut at $arious stages thedeformation may eceed the strength of the rock so that it does not bend butfractures instead and undergoes displacements along faults.

4. The distortions (lateral and)or with up&down mo$ements" of crustal materialscombine with physical and chemical reactions between atmospheric constituents(mainly oygen and water" that weather (breakdown and)or dissol$e" rocks which

are then eroded, transported (by running water, ice, wind, gra$ity" and depositedin low surficial locations on land or in water bodies (oceans and lakes". Theseactions contiually modify the shape of the land and ocean surfaces producing awide range of continental and oceanic landforms (mountains, $alleys, plateaus,plains, $olcanic edifices, etc.", de$eloping a wide $ariety of landscapes.

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This illustration shows the four fundamental continental landforms;

This is a panorama of many of the common landform types;

=andforms de$elopment is often a comple process re<uiring long time periodsduring which specific landform types take shape, e$ol$e, and disappear. actorsin$ol$ed, besides time, are the actions of shaping forces such as running water,etc., the type(s" of climate a region eperiences (can change from humid to aridor re$erse", the nature and resistance to erosion of the $arious rock type present

and their structural configuration, the history of deformation o$er time, and risesand falls of the regional ele$ations (through isostasy & a tendency for the crust toassume altitudes that maintain balance e<uilibrium! within the Earthsgra$itational field". *odern theories of landform de$elopment are di$erse butmost trace their ideas back to 1th +entury specialists (9eomorphologists" suchas Billiam Fa$is. Bhile the details ha$e changed, his notions of landform cyclesremain largely $alid. This illustration generali3es the changing landscape in ahumid en$ironment;

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The starting point is the emergence of flat&lying sedimentary rocks from the seaas a coastal plain made up of flat&lying sediments. Streams that de$elop duringGouth follow the gradient (slope" from the highest land to the ocean shoreline

start to cut down narrow, steeper&walled $alley slopes. The progression then istowards $alley widening that lea$es uplands as hills and mountains. :y a stagecalled *aturity, the uplands ha$e been car$ed by enlarging $alleys so as to lea$eonly the original uplands at narrow ridges. Thereafter, as /ld #ge is approached,gra$ity&dri$en erosion by sheet flow (thin spread of water o$er a surface" and bymass&wasting (loose rock mo$ements" o$er the mountain surfaces slowly reducethese uplands to local hills with the landscape. The mountain terrain, ha$ingbeen generally lowered o$er time, finally becomes one of low relief (smalldifferences in ele$ation". Fa$is called this end product a ApeneplainA, a term notnow used ecept as an ideali3ation of what a final stage would be like- uplift(block diagram 9" is likely to occur before then, which causes a repeat of the

o$erall process cycle (re@u$enation". %f the rocks had been inclined (folded" rather than flat, the cycle would ha$e been modified, with hard, less easily erodiedrocks maintaining the upland mountains. e@u$enation has now acted on thepresent&day #ppalachian *ountains such that the ridges (see page 6&>"represent hard rocks and the $alleys occur in softer, more easily remo$ed rocks.

# different cycle can be specified for erosion under arid climatic conditions. Theend result depends on the structural nature of an eroding region. /ne case,

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shown below, relates to mountains uplifted along high angle faults (producingAblock&fault mountainsA" such as in the :asin and ange of the western D.S. (seepage 6&H". ere the se<uence of change seems simple; from the starting point of high mountains and low $alleys, the mountains wear down and their erodeddebris fill the $alleys, so that the final outcome is a subdued topography with low

remnant uplands (pediplains" and deeply filled, raised $alleys.

7. Since its beginning, the Earth has been an acti$e, dynamic planet thateperiences continual changes in its interior and especially its ouer lithosphereand surface. %ts continents ha$e grown relati$e to oceanic crust and ha$e shiftedin position (as referenced to a standard global surface" the mo$ements are calledcontinental drift. *ost of Earths history (epressed se<uentially as the 9eologicTime Scale" is best deciphered from its rocks, particularly sedimentary ones, thatrecord se<uences of modifying e$ents (deduced in part through patterns of lifeforms usually as fossils! changes (by e$olutionary processes" and from rockage measurements (based on fied rate radioacti$e decay".

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6. The Earths surficial en$ironments operate as a comple, interrelated systemof units and features best categori3ed in terms of the physical)chemicalcomponents of the Geosphere. Atmosphere, Hydrosphere, and Biospherepowered by solar and internal heat that interact at, @ust below, and abo$e theglobal surface to produce a series of conditions that aid, inhibit, and otherwiseaffect Humans and all li$ing creatures. The study of how these ASpheresA

interact, echange energy, and produce positi$e and)or negati$e feedback iscalled Earth Systems Science. This $ersion of the definiti$e :retherton diagramsuggests some of these inputs and effects.

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%n the remainder of this page, we will eplore in more detail three primary topics;The ock +ycle- 9eologic Time- late Tectonics. The sub@ect of =andscapes ismore fully treated in Section 18, entirely de$oted to =andforms from both groundand space prespecti$es.

The Rock Cycle

To discuss this sub@ect, we will use these two diagrams- the first (similar to theone presented near the top of this page" shows again what is known as the ock+ycle (obser$ed changes from one rock type and mode of origin! into other types" and the second indicates the names of the ma@or rock types in each of the

three main groups; %gneous- Sedimentary- *etamorphic;

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To assure you are certain of what a rock is, we define it simply as anassemblage of one or (most commonly" two or more minerals (specific chemicalcompounds" that form a part of the Earths solid body. # ArockA normally connotesan indi$idual AspecimenA & one that can be held in ones hand or is larger butdetached from its outcrop (eposure of the rocks source" so that it has $isibleboundaries. The dependence on mineral composition and teture in naming rocktypes is best illustrated as applied to igneous rocks, as in this diagram;

5ey parts of the ock +ycle (+" in$ol$e magmatic)$olcanic)metamorphicprocesses that produce crystalline rocks, the actions of water and air indisintegrating rock materials and transporting)depositing them as sedimentswhich lithify into sedimentary rocks, the dynamic forces that deform rocks, and

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speciali3ed actions like wind, wa$es, and ice in modifying rocks at the surface.The subsurface crust is altered by heat and pressure- the surface byphysical)chemical weathering and erosion (B)E, namely Beathering)Erosion".*uch of the + is most acti$e where tectonic plates meet; new rocks form- oldrocks are changed.

The general pattern followed in the + is shown in the first of the two diagramsat the beginning of this subsection. %t can be summari3ed $erbally in thisse<uence; *olten rock &&&I %gneous ock &&&I B)E of igneous rock &&&ISediments &&&I Sedimentary ock &&&I Sedimentary and %gneous ocks, onburial, eperience heat and pressure &&&I *etamorphic ock &&&I further heating)pressure &&&I *olten ock. The process can then repeat. /ne addedfeature; any igneous, sedimentary, or metamorphic rock at)near the surface canundergo B)E &&&I Sediment. The energy dri$ing the + comes from threeprincipal sources; 1" Solar & the Suns radiation pro$ides kinetic energy to mo$eair and water)ice- 0" 9ra$itational & rock and water mo$ements downslope- >"

Thermal & trapped heat emanating mainly from the Earths interior (where thesource is radioacti$e decay" or from thermodynamic processes (compression,change of state".

*olten rock is called magma if it remains below the surface and lava if it reachesthe surface. *ost magma is generated in the crust (mainly upper lithosphere"-some may deri$e from the uppermost mantle (asthenosphere" by upwelling andpartial melting. *agma reaches the surface as $olcanoes or $olcanic outpouringsprimarily where 1" ocean plates spread (at ridges"- 0" an oceanic plate di$esunder (subducts" another plate, inducing melting into magma that rises upward,often to the surface, >" under continents that eperience crustal or mantle

heating (magma may remain below surface as batholiths", and 4" where amo$ing plate passes o$er a mantle thermal plume, causing a hot spot, andmelting. The two main igneous rocks are Granite & which forms within continents,intrudes upwards but remains under the surface & it forms light&colored and largefeldspar and <uart3 (minerals" crystals- and Basalt & which etrudes as la$as onboth ocean floor and continental surface and rapidly cools & it is dark because of amphiboles)pyroenes (greenish&black" with gray feldspars in small crystals.

#tmospheric weathering (0/, /0, and +/0and near surface weathering mainlyby water affect all rocks. hysical weathering & still and mo$ing water, wind,gra$ity, and human acti$ities & fractures, grinds, and flakes rocks into particles.+hemical weathering produces acid conditions that dissol$es rock (eample;sinkholes in limestone". Erosion loosens and mo$es particles (solids ? clastics"and breaks rock down by solution. These become sediments that are transportedby ri$ers, ocean wa$es, wind, sliding ice, gra$ity to collect in settling basins bydeposition. Sediments tend to accumulate in layers and con$ert to sedimentaryrocks by lithification & pressure s<uee3ing (compaction" and cementing. *ainsedimentary types are; Conglomerates/Breccias (pebbles and clasts fractionsof an inch up to boulders! held in a finer&grained matri"- Sandstone ($isible

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grains of <uart3, feldpsar" Shales (fine particles including clay minerals",$olumetrically the most common type- Limestones (chemical precipitates andbiochemical animal)plant carbonates- and Coal (decayed plant matter".

*etamorphic (Achanged formA" rocks form from action of heat and pressure on

pre&eisting rocks. Shales (themsel$es finely layered" follow this progression withincreasing T and ; Shale &&&I Slate (fine&grained, brittle" &&&I Schist (micaflakes" &&&I Gneiss (light and dark crystal banding" &&&I melting to a magma.=imestone &&&I Marle- Sandstone &&&I !uart"ite- Basalt &&&I Amphiolites or Serpentine. *ost metamorphic rocks de$elop distincti$e foliation or lineation-some may inherit e$idence of layering if deri$ed from sedimentary rocks.

+/'T%'DEF /' TE 'EJT #9E.

rimary #uthor; 'icholas *. Short, Sr.

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G**1!+ T!'

Bhen one mentions Ageologic timeA to a geoscientist, that person immediatelystarts to think in terms of millions to billions of years. The Earth organi3ed as alarge accreted body between 4.7 and 4.6 billion years ago. The unit of time

measurement applied to geologic history remains the year , which probably hashad only limited lengthening (from slowdown in Earth rotation" since thebeginning. or practical purposes, we continue to work with the standard year of >67.07 days (although the days were once shorter as the Earth rotated faster inthe early days of Earth history".

The rocks at the Earths surface or accessible (e.g., by drilling" in its shallowinterior ha$e a $ariety of ages as one mo$es from place to place. The <uestionbecomes; ow does one know at least the approimate age, i.e., how muchearlier in the past did this rock or rock unit (e.g., a layer" become initiallyemplaced (it may be mo$ed by erosion or crustal deformation, etc."C Two

solutions to the <uestion are; 1" determine its relati$e age and estimate its time of formation by approimation techni<ues- and 0" use some sort of absolute timedating method.

elati$e age determination in$ol$es some important rules; 1" the =aw of Dniformity (Kames utton";The resent is the 5ey to the ast- this means thatprocesses we obser$e in todays world likely operated throughout the past, backe$en billions of years ago- 0" the =aw of Superposition; Dnder mostcircumstances when sedimentary layers are deposited in a se<uence, the lowestin that se<uence was deposited first and is the oldest whereas the highest waslast deposited and is the youngest (this may become spatially AuntrueA when

rocks are displayed by faulting or se$ere o$erfolding"- >" the =aw of +ross&cutting; any geologic feature (igneous intrusion- fault, etc" that cuts into)acrossrock units must be younger than these units- 4" the =aw of aunal Succession; ina se<uence of rocks of significant thicknesses, there may likely be remains of animals)plants (fossils" that show some systematic e$olutionary progression-most commonly the change is towards compleity and di$ersity and followsmorphological and taonomic modifications.

Dntil the 1Hth and 1th +enturies, the age of the Earth was estimated more frombiblical interpretations than from scientific determinations. Then, following utton,=yell, =amarck, Farwin and others two things were reali3ed; 1" it takes thousands

to millions of years to deposit layered sedimentary rock units of thicknesses inthe 12s to 122s of meters realm- and 0" progressi$e e$olutionary changes alsotake millions of years for significant ad$ances in the de$elopment of genera andspecies to become recogni3able. :y the end of the 1th +entury, Earth hadAagedA from the 4224 :+ estimate by :ishop Dsher to millions of years. %n the02th +entury the age passed two billion years and with more precise methods(radiometric- see below" 3eroed in on the present $alue near 4.6 billion years.

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The most indicati$e method for reaching the billion year age category was simplyto measure the thicknesses of units in one place and estimate the time to depositthem (millions of years", then go elsewhere and find at least some of the sameunits that had different units below or abo$e them, which had to be older or younger. This in$ol$es correlation of units (see second 9rand +anyon diagram

below" based on specifying in the se<uence something in common from place toplace, as for eample certain animal)plant fossils that are the same or similar, or distincti$e rock types in the same se<uences. :y roaming o$er a continent andbetween continents, se<uences were recogni3ed, described, and matched withse<uences elsewhere that had new member units, within, up, or below. Thisleads to a general AworldwideA Geologic Column that tries to account for all thedeposits laid down during gi$en time inter$als (spans" in $arious locations thatcan be matched and then epanded by o$erlapping correlation (see below".

#round the turn of the 1Hth +entury into the 1th, $arious geologists working indifferent regions who were adept at stratigraphic analysis (recognition of layers

that had characteristic time markers such as fossils" began to publish their descriptions of the se<uences they studied. /thers found different se<uencesand)or some of the same se<uences in the descriptions. +ombining thegeographically separated obser$ations, using correlation to tie units of the sameage to the se<uences, a composite se<uence (which included filling gaps whererocks of an age in one region were missing" known as the 9eologic +olumn wasbuilt up. #s the 9eologic +olumn grew, estimates of their ages were made usingmainly deposition rates. %ndi$idual se<uences within the column were assignedtimes in the past which resulted from the column estimates.

%t became con$entional to gi$e a name to a se<uence that seemed to represent a

long span of time but had certain diagnostic properties (e.g., a collection of lifeforms that, while e$ol$ing, possessed traceable similarities". These se<uencesbecame #eriods in a temporal&stratigraphic nomenclature and all rockscontained within the se<uence made up a System. Subdi$ision of eriods intosmaller time spans yielded $pochs, with their ocks being Series. :roader di$isions of time made up of a some number of eriods (each younger oneo$erlying an older eriod & =aw of Superposition" were called $ras. 'ames gi$ento eriods either had some geographic significance (the +ambrian eriod wasfirst described and measured in +ambria within the :ritish %sles" or at the Era=e$el were defined by an appraisal of the dominant life forms and their stages of e$olution (the *eso3oic means A*iddleA A=ifeA 3o& is part of a 9reek wordpertaining to life".

rom this approach, a system for epressing geologic time and namingsubdi$isions has emerged, as shown in this diagram;

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This scale has many subdi$isions o$er the last 622,222 million years, since theserocks are well preser$ed in parts of the world. #ll rocks older than the beginning

of the aleo3oic (Aancient lifeA", whose oldest period is the +ambrian, are said tobe recambrian & a general term, that is now undergoing further subdi$isions.The bulk of geologic time (about H8L" is recambrian, as shown in this diagram

Bith the introduction of this nomenclature, we can now look at two figures thatuse deposition rates, superposition, and correlation to build up a regional9eologic +olumn co$ering rocks in #ri3ona and Dtah. The first shows the+olumn as determined from rocks eposed within the 9rand +anyon.

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The +olumn units are well displayed in this photo showing the 9rand +anyonfrom the stratigraphic base cut by the +olorado i$er to the canyon rim;

Se$eral comments are in order; 1" the hori3ontal rocks all fall within thealeo3oic Era- since they are hori3ontal, they rest in the same positions as whendeposited & they ha$e not been folded- 0" some rocks within indi$idual eriods

31



are distinct from one another- they constitute %ormations (mappable units thatare named from where geographically! they were first described"- >"representati$es from some eriods or Epochs are missing & either they werene$er deposited in the ancient seas that produce the ormations or if depositedha$e since been eroded away & this gap represents a hiatus termed an

Unconformity (this embraces both the missing strata and the surface of contactbetween the two rock age groups that together point to a break in depositionalcontinuity"- 4" rocks below the aleo3oic are recambrian- the upper group aremetasedimentary but tilted (folded" indicating they were deformed in some typeof mountain building (Orogeny ", beccame partially eroded and were then co$eredwith the lowest aleo3oic units, making an #ngular Dnconformity - 7" these inturn rest on metamorphic rocks (mostly schists and gneisses", much older withsome upper units ha$ing been remo$ed by erosion (reaching into lower le$els of the crust" to form a 'onconformity- 6" the metamorphic rocks were intruded bygranite, which by the =aw of +ross&cutting must be younger- and 8" e$en now,rocks at the surface (top of the column" are being eroded and probably were

undergoing erosion since the aleo3oic- this absence implies that *eso3oic and+eno3oic rocks are missing, either through erosion or absence of depositingseas- if at some future time seas roll into the region a new unconformity willde$elop on the gradually submerged land surface.

The net diagram shows how the 9eologic +olumn has been compiled for thisregion using correlation;

32



The link between the 9rand +anyon and :ryce columns is the 5aibab=imestone. :ryce contains *eso3oic units, of which the Kurassic 'a$a@oSandstone is most distincti$e- the 'a$a@o sst ser$es to link with the top of thecolumn in Mion '. That sandstone unit is near the base of the section at :ryce+anyon which preser$es Dpper (higher" *eso3ic Dnits and an early Tertiaryormation & the Basatch & in the +eno3oic. So the composite of the threecolumns or sections has representati$e deposits in eriods from the recambrianthrough the aleo3oic and *eso3oic into the young +eno3oic.

The skills of stratigraphers o$er the last 022N years has produced a generalgeologic column and a time scale that pro$es to be <uite accurate. :ut thisaccuracy had to be confirmed by some independent method that measuresasolute time. That had to await the disco$ery of radioacti$ity in the late 1th

33



+entury followed by the reali3ation that radioacti$e elements (as isotopes" decay(their nucleus is changed to another radionuclide of the same element or morecommonly to new elements" at $ery precise fied rates. The decay is said to beeponential (for eample, a series proceeding as 1&&I0&&I4&&IH&&I16&&I....710&&I120H&&I... is eponential". or eample, some gi$en amount of the radioacti$e

form of otassium, 542

will ha$e half its atoms come apart to form radioacti$e #rgon #42 o$er a long finite time ? 1.071 billion years. (#n element with asuperscript is an isotope whose mass number is gi$en by the superscript- #rgonhas two isotopes istopes ha$e same number of protons Oa particular atomicnumber that defines the element speciesP but differing numbers of neutrons!,thus #> and #42!, with the latter ha$ing one additional neutron". +onsider thisdiagram;

alf the otassium42 is gone after 1.071 billion years- half remains. 'ow if another 1.071 billion years elapses while the mineral containing the otassium(se$eral isotopes", then in 0.720 billion years only 1)4th of the original 5 42 willremain and a larger amount of #42has de$eloped. The clock on dating beginswhen the original potassium is incorporated in the rock- it is assumed that noinitial #rgon, a gas, was present. #ssuming none of the # 42 escapes o$er time,then a geochronologist need only measure (using a mass spectrometer" theamounts of 542 and #42 now present in the rock to set up a ratio and to use the

decay rate (gi$en as a half!life, the time re<uired for half of any of theradioisotope to decay" to determine the age. %f that ratio is 5 42)#42 ? 1)Hth, theage would be >87> million years & the time between incorporation of theotassium in the rock (likely, in the feldspars making up a granite" and thepresent.

Qery accurate ages of incorporation are possible using radiometric dating,pro$ided none of the otassium and #rgon isotopes escape or no element

34



contamination occurs. There are a number of radioacti$e element that ha$e their own decay schemes. adioisotopes of Dranium (D" decay at $arious rates toisotopes of other elements (e.g., adon" and a se<uence of one to se$eral steps(Fecay Series" and ultimately to isotopes of =ead (b". The element ubidium(found in micas" decays to Strontium. Some elements decay o$er short half lifes

and are limited to dating younger rocks (+arbon isotope decay works well if rockwood- other organics! is less than a half million years old"- others are especiallysuited to determining recambrian times. %f a shale is intruded by a granitic dike(narrow tabular cross&cutting body", the two rock types can be dated by differentradioisotope methods, so that the time when each e$ent took place can be fiedfairly accurately.

Thus, since the early 02th +entury geoscientists ha$e had a powerful tool toreconstruct when different specific e$ents took place in a comple assemblage of rocks, so that a precise geologic history can unfold. The table below summari3esa generali3ed history of, mainly, the primiti$e Earth.

/$er the long span of geologic time, the sedimentary rocks of different typesha$e changed in their relati$e proportions, as indicated in this diagram (note;

35



mudstones are e<ui$alent to shales- arkoses and greywackes are sandstonesderi$ed from granites and basalts respecti$ely";

The oldest dated mineral, a 3ircon from #ustralia, is age&fied at 4.1 billion years,but most early ages for rocks fall around >.6 b.y. Thus most of the Earthsoriginal, and some subse<uent, crust has been destroyed (remelted- subducted-

broken down by weathering". Bhen oygen was nearly absent from theatmosphere, the most characteristic rock type was :% (:anded %ron ormation"-its production consuming any oygen released. #s photosynthesis in plantsemerged as a working process, oygen increased, producing iron oides in theform of ed :eds- then also carbonate rocks became commonplace insedimentary se<uences.

The most important e$ents, from the human perspecti$e, ha$e been the originand time of appearance of the first li$ing forms, and the subse<uent de$elopmentof the ma@or phylla and orders of life on land and sea. The first indications of lifeetend now to earlier than >.7 billion years ago. Early life was single&celled &

procaryotic. *ulti&celled life & eucaryotic & appeared in the recambrian. Thegreatest di$ersity (AeplosionA" of life occurred at the close of the recambrianinto the +ambrian eriod. Since then at least 6 mass e"tinctions (significantfraction of all life types at the time diminishes or disappears" ha$e occurred. Thetime se<uence of life on Earth is depicted in this AcartoonA, in which principles of e$olution go$ern the progression and emergence of new phylla;

36



The abo$e taken from A=ife in the Dni$erseA, Ste$en Beinberg, Scientific #merican, /ct. 14

*uch of the life topics abo$e is eamined in more detail on page 02&10.

uman and animal life, as well as many of the modern landscapes andlandforms, ha$e been strongly influenced in the last fi$e million years by a seriesof continental glaciations. :ecause of this great surface&modifying phenomenon,se$eral paragraphs and illustrations are incorporated here within the 9eologicTime category.

37

http://rst.gsfc.nasa.gov/Sect20/A12.html

http://rst.gsfc.nasa.gov/Sect20/A12.html



#bout fi$e million years ago, global temperatures began a slow, then faster decline, as indicated by the sensiti$e /1H)/16 ratios in certain sediments and inice. :y about 0.2 m.y., the first signs of a worldwide %ce #ge began to appear.rom then until today, temperature measurements indicated many cycles of warming and cooling.

Furing this time, referred to as the leistocene (the most recent 17222 years tothe present is called the olocene", there were at least four ma@or inter$als of continental scale ice co$erage o$er about >2L of the Earths land masses. Theduration of etensi$e ice co$erage is between 72222 and 122222 years, withinterglacial (warm" inter$als of similar duration. %n Europe, the glacial stages aregi$en the names shown here;

38



Each glacial ad$ance greatly modified landscapes it co$ered, and both glacialand interglacial times were influenced by climatic changes that affected surfaceswell beyond the periglacial en$ironment. (The tropics were altered in glacial timesbut during interglacial periods subtropical conditions were present in todayssubarctic 3ones." *ost of the earlier glacial geomorphic effects were destroyed or buried by the last glaciation, which co$ered the northern hemisphere as shownhere- below that is a more detailed look at 'orth #merican glaciation during thisBisconsin time.

39



#t least four glacial ad$ances co$ered 'orth #merica in the last 0,222,222 years.These and the inter$ening interglacials are named in this diagram

This map of the D.S. *idwest indicates that deposits from each of the ad$ancescan be found. This map also suggests that all the four glacial ad$ances reachabout the same southern limits.

40



Gellow and green denote 'ebraskan glaciation- blue 5ansan- purple %llinoisian-and white with markings, the youngest, or Bisconsin glaciation.

The cause(s" of leistocene glaciation has(ha$e" not been fully ascertained tomost geoscientists satisfaction. Systematic (cyclic" $ariations in solar output (the*ilanko$itch cycles" seem to be a factor but these ha$e been routine for millionsof years. +hanges in +/0 output, which alter temperatures, may be another input. #lternating free3ing o$er, and then thawing, of the #rctic ocean could playa role. erhaps decisi$e as a reason for the onset of glaciation in the past fewmillion years is the @oining of 'orth and South #merica by the land bridgeassociated with the %sthmus of anama & this was finali3ed about > million yearsago. That completely changed the circulation patterns in the #tlantic and acificoceans, which could led to cooling of #rctic waters and initiation of northern

hemisphere ice formation on a grand scale.

%n the northern hemisphere at mid to high latitudes, most modern landforms owesome etent of their de$elopment to direct or indirect influences of leistoceneglaciation. *inimal effects in #frica probably facilitated the e$olution of the earlier hominids. The migration of the $arious AhomoA species was partly directed bychanging climates. *odern man, who first appeared about 122,222 years ago,was mo$ed about by later stages of the Bisconsin ad$ance. The beginnings of ci$ili3ations about 12222 years ago owe much to the onset of the presentinterglacial inter$al (see page 02&10".

41



#late Tectonics& Mountain Building& ContinentalGro'th/Mo(ements

# good re$iew of these topics which supplements the co$erage below has beenprepared online by the D.S. 9eological Sur$ey.

#s the 02th +entury began, ma@or unsol$ed problems in understanding theEarths geology included the distribution of rock type by age and by structuralstate, the causes of mountain building and other modes of deformation, thedistribution of earth<uakes and $olcanoes, and the nature of the seafloorscomposition and geologic features. This worldwide map shows threefundamental rock units; 1" ancient recambrian igneous&metamorphic rockseposed as Shields (red", 0" mostly flat&lying sedimentary rocks (orange", and >"folded)faulted rocks in mountain belts (brown"

rom Tarbuck R =utgens, The Earth, >rd ed., 12

*ountain belts are characteri3ed by se$eral distincti$e geologic features; 1" theyusually ha$e significant topographic epression & the surface consists of peaks,ridges, and inter$ening $alleys- 0" the sedimentary rock units are generally non&hori3ontal & the layers dip (incline"- >" there commonly are associated igneousand metamorphic rocks- 4" large parts of the crust ha$e been broken into blocksand displaced along faults. Two hallmarks of many mountain belts (also calledorogenic units" are greenstones (metamorphosed basalt that represents oceaniccrust subducted below an o$erlying crustal block" and ophiolites (deep crustal or mantle rock brought upwards towards)to the surface". These are shown here asseen from space;

42

http://pubs.usgs.gov/publications/text/dynamic.html

http://pubs.usgs.gov/publications/text/dynamic.html



Be will concentrate our discussion of late Tectonics and continental growth on'orth #merica as a definiti$e eample. #s radiometric ages were determined for the shield&like rocks within the continents which were either eposed at thesurface, underlay the flat rocks, or were within the interior of the mountain belts,patterns of age inter$als were determined, as shown in the net two figures.

43



rom =utgens and Tarbuck, $he Earth, >rd Ed.

The rocks older than about 722 million years ha$e been called the AbasementA &a term that suggests they are found at the AbottomA of the accessible crust. Their age and distribution ha$e been interpreted to mean that the continents had

44



somehow grown (enlarged" around their oldest crustal components (nuclei" byaddition of rock assemblages & in some instances these were crustal landmasses(terranes" de$eloped elsewhere with their own characteristic age parameters.The additions are mainly through collisions of crustal masses resulting from platetectonic mo$ements throughout the ancient past- these accreted (or

tectonostratigraphic" terranes are discussed in the second half of Section 18. Theepanding continental nuclear units coalesce to become part of the AcratonAwhich consists of both eposed (as a AshieldA" and buried basement rocks(mostly now metamorphic and igneous". *aps of these units shown abo$e comefrom two sources, show different subdi$isions, and hence do not perfectly agreein distribution and age among specific added components. The orogenic(mountain&building" units known as the #ppalachians and the +ordillera make upthe outer parts of 'orth #merica and are the youngest (less than 722 millionyears" of the ma@or components of the continent (which lies embedded in the'orth #merican late". %n these maps sedimentary rocks deposited o$er the past772 million years that lie between the eastern and western mountain belts in the

continental interior ha$e been Aremo$edA so as to re$eal the basement units theyo$erlie.

:y the latter half of the 1th +entury, studies of the #ppalachian *ountains andothers led to this general picture of a linear, wide se<uence of all three types of rocks that had been deformed and may still show topographic e$idence of differential erosion producing present&day mountains.

/ne part of the mountain system consists of folded)faulted sedimentary rocks.These appear to ha$e been deposited on the other part, deformed segments of the basement, much being recambrian, both with younger granitic intrusions.

#ttempts to eplain this mountain structure led to $arious hypotheses, chief of which were put forth by Kames all and Kames Fana in the later 1H22s from their studies of the #ppalachians. %n this model, there were two regions near acontinental margin that downsank to form Geosynclines & troughs that couldrecei$e o$er time deposits of sediments that eceed 17222 meters (72222 ft" inaccumulated thickness.

45



%n the geosynclinal model, from time to time these sediments (con$erted by burialto sedimentary rocks" would be s<uee3ed by compressional forces causing upliftand folding of mountains o$er at least part of the length of the linear trough(s"(typically 1222&>222 miles- widths around 722 miles", followed by erosion(unconformities" and renewed deposition. inally, the entire geosynclinal belt was

sub@ected to intense compression leading to the main phase of orogeny (mountain&building" and general uplift that o$er time causes remo$al of some of the mountain units through erosion, in places eposing the basement.

owe$er, as the 02th century progressed and new information about mountainsand continents accrued, problems with this model were identified. #lfredBegener, a European meteorologist, noted that if continental outlines (includingsubmerged edges near shore" for Europe, #frica, 'orth #merica and South

#merica were placed net to each other (say, by cutting them out like Apaper dolls", these continents show a remarkable fit, shown here.

46



Begener hypothesi3ed that at some time in the past those continents had beencon@oined as a single supercontinent he called angaea. Then they broke apart(continental split" and starting mo$ing away from one another until reaching their present positions. This was continuous but is shown here in three stepsreprenting stages since breakup began near the end of the aleo3oic. e called

the process Continental )ri*t and speculated that thermal currents in the mantlemay pro$ide the dri$ing forces. E$idence he cited to support the idea includesstructural continuity (mountain systems on continental pairs match when the fitrestores their original positions, glaciation effects on indi$idual continents beingfound continous when two continents are re@oined, and, strongest of all, presenceof the same animals)plants (as fossils" of types that could not swim acrossoceans or float far by air.

47



angaea itself further ruptured into two continents & =aurasia (north" and

9ondwanaland (south", each of which split further into the present geographiclayout. The net illustration is an oft&cited (this $ersion came from a D.S.9.S site"panorama showing the positions of the continents from early angaean breakupto the resent.

48



The general time frames for specific separations and collisions in$ol$ingangaea is summari3ed in this diagram (mya ? millions of years ago";

/ne can ask the <uestion of how angaea itself came into being. *ost modelsdraw upon paleomagnetic (see this %ntro page, near bottom" and other e$idence

49

http://rst.gsfc.nasa.gov/Intro/Part2_1a.html




that suggest $arious earlier continents & with little resemblance to present&dayones & assembled by plate motions o$er the globe that caused them to con$ergeinto =aurentia and 9ondwanaland and e$entually into angaea. # group in 'ewMealand offers this history for a >02 million year span;

%t is likely that se$eral such assembly&breakup&reassembly&breakup.... episodes &each lasting hundreds of millions of years & ha$e occurred e$er since platetectonics began (roughly 4 billion years ago". Those interested in moreinformation on the se<uences of drift positions o$er last half billion years thatha$e now been reconstructed should $isit this website produced by the 9eologyFepartment at the Dni$ersity of Bisconsin at 9reen :ay.

%f present day trends continue, one can etrapolate the drifting of continents intothe future such that in about 072 million years a new super&angaea will ha$ereassembled. This is an Aeducated guessA as to the configuration;

50

http://www.uwgb.edu/dutchs/platetec/plhist94.htm

http://www.uwgb.edu/dutchs/platetec/plhist94.htm



:y the 172s the geosynclinal model had been discarded but continental driftremained in fa$or. # new paradigm was needed. # series of obser$ations led tothe general model of #late Tectonics which became a ma@or re$olution ingeological thinking about the realities of a dynamic Earth.

The first bits of eplanatory e$idence came from disco$eries about the deeper ocean sea floor. #erial geophysical flights across stretches of the oceanunco$ered an unepected magnetic phenomenon. E$idence found by magneticproperties analysis of the etruded oceanic basalt permitted establishment of thepolar directions at the time the basalt sample crystalli3es. (The basalt containsmagnetite and other iron minerals that act like Aminiature compass needlesA thatalign so as to point to the ole arbitrarily called 'orth! where magnetic lines of force in the Earths magnetic field enter the planet at the time of la$asolidification." Studies of samples at different distances from the ridge crest foundthat the 'orth and South *agnetic oles re$erse their polarity (i.e., thegeographic South polar region becomes the entry point for magnetic lines of

force and 'orth the eit point" o$er time inter$als of less than a hundredthousand to a few million years (on a$erage e$ery 022222 years, lea$ing the fieldat minimum strength o$er about >222 years" during the re$ersal period. Bhensur$ey flights passed across *id&/cean idges, patterns like the one belowwere registered- each stripe indicates that for the time basaltic la$a etrudes (atrates of 7 to 02 cm)year" the enclosed magnetic minerals for the full inter$alneeded to produce the width of a stripe (12s to 122N km" are pointed either totodays magneti3ation (normal '&S- positi$e" or to the opposite polarity (re$erse'&S- negati$e".

*ore about this and other rele$ant information applicable to 9eology has alreadybeen re$iewed for you in the subsection of the %ntroduction that dealt with

9eophysical emote Sensing

/f special significance is that the patterns on either side are mirror images of each other. This can be eplained by assuming that new ocean crust pours out atthe ridge and spread away in both directions o$er the span of time in which onepolarity & normal or re$erse & is operati$e. Spreading rates to either side areabout e<ual. The series of normal&re$erse polarities alternate o$er time gi$ing the

51





symmetric pattern obser$ed (not really black and white & that is for depictionpurposes".

#bout that time, deep sea dredging and later drilling brought up samples of thebasaltic ocean crust which could be dated radiometrically. /$er the years enough

parts of the oceans floors were reached, sampled, and dated. The general trend,when data points were plotted, was for (magneti3ed" stripes of basalt to beyoungest at the ridges and oldest where ocean floors meet continents. This is theo$erall picture.

rom amblin, Earths Fynamic Systems, 6th Ed., 11

This surprising mechanism of adding new material at ridges and ha$ing surficiallayers mo$e away from the *id&/cean idges (found in the acific and %ndian/ceans too" was independently, and almost simultaneously named by Fr. arryess (rinceton" and Fr. obert Fiet3 ('/##" as Sea %loor Spreading. %tstarted others to thinking about how it works and the conse<uences applied tothe Earths eterior. #s new data from geophysics on earth<uake epicenters

(surface pro@ections of source areas at depth" and better plots of $olcanic acti$itywere shown on maps, this general pattern became ob$ious (see also the tworele$ant illustrations on page %ntro 0&1c";

52

http://rst.gsfc.nasa.gov/Intro/Part2_1c.html




rom amblin, Earths Fynamic Systems, 6th Ed.

The way to eplain these obser$ations now opened fast for geoscientists. 'o oneindi$idual is credited with Athinking upA all the basics of late Tectonics- manycontributed $ital e$idence and inno$ati$e operational models during a relati$elyshort period in the 162s onward. The essential idea starts with this assumptionin an attempt to eplain the earth<uake and $olcanic distributions; The present&day Earth outer shell is broken into 6 ma@or plates (co$er large areas" and somesmaller ones. They ha$e se$eral types of boundaries (see below" and are about022 km thick. (%f a large plate could be ApluckedA from the Earth it wouldresemble an orange peel, being cur$ed as a segment of a sphere". The platesconsist of a se<uence of rock types, either basaltic crust and %ron&*agnesium

upper mantle or continental crust o$erlying some basaltic crust and mantle,which makes up the relati$ely rigid rocks that comprise the Lithosphere. :elowthe lithosphere is mantle rock soft enough (through heat" to allow the lithosphericplates to AglideA laterally across parts of the globe. This map shows todays ma@or and minor plates now identified as separate mo$ing bodies- o$er time in the pastand pro@ected into the future, the plates si3e and location will $ary as indi$idualplates grow or are consumed;

53



Today, the plates are mo$ing in different directions and at $elocities of a fewmillimeter to centimeters per year (see this page."

our types of plate boundaries or margins ha$e been recogni3ed;

:oundary type # is di$erging- at a *id&/cean idge, la$a etrudes in twodirections as it adds to ad@acent plates. This is the region where the main dri$ingforce that mo$es plates apart is applied. :oundary : occurs where two oceantype plates (no nearby continental crust" con$erge head on. /ne plate is forcedunder the other, this is called suduction in which the underthrust plate graduallymelts and dissipates (becomes part of the mantle rock" when pushed to

54





increasing depths. The process leads to indentations of the crust thatoceanographers call trenches- the deepest on Earth today is the *arianasTrench in the acific, whose ocean floor top is nearly >7222 feet (12 km" beneathsea surface. The + :oundary refers to a con$erging margin where continentalcrust meets continental crust on the second plate. :oundary F is somewhat

different & it does not de$elop at a di$erging or con$erging boundary but is either at a plate edge where two plates slide past along transform faults or is one of aseries of transform faults that aid mo$ement within a plate.

Be are now ready to define the interaction of plates through this schematicdiagram;

*elting of the mantle, mainly near the top of the heated asthenos%here (3onewhere the rock is $ery hot, but soft like tar!, yet remains solid", causes la$a tomo$e upwards into a long linear fracture system that builds up as a *id&/ceanidge- the two plates on either side are di$erging. To the left one of these oceanplates meets another and subducts. rictional and residual heat producemagmas on the plates up side that reach the surface as la$as which accumulateinto $olcanic structures. These produce &sland #rcs, constructed around the$olcanoes- %ndonesia, Kapan, and the #leutians are three eamples. To the right,the other plate meets a continent&bearing plate and also subducts. *elting againproduces magmas that intrude near the continental margin and surface as$olcanic la$as (either flows or $olcanoes"- the #merican +ascades are of thisnature. inally, within the continental upwelling con$ection currents may beforcing the continent to pull apart as a rifting 3one which in time may split thecontinent into two or more parts (eample; angaea".

The diagram below ties this type of plate margin into the rock cycle.

55



rom Tarbuck and =utgens, The Earth, >rd Ed.

The nature of the dri$ing forces seems to be tied to slow mo$ements something

like currents (analogy; those that stir up the surface in a swirling cup of hotchocolate" of $ery hot, plastic&like (but still solid" mantle rock. These in$ol$e heattransfer by con$ection. Some e$idence suggests these con$ection currents(shown below" originate near the mantle)core boundary. /ther signs indicateshallower origins or perhaps a secondary set of currents in the upper mantleonly.

Kust to emphasi3e the characteristics of the plate tectonics model, this is the third$ariant we ha$e shown on these two pages. The upper diagram follows the full

56



mantle con$ection hypothesis- the lower diagram show the part of the cycle thatincludes the ma@or upward flow that dri$es sea floor spreading in the upper half.

rom *c9eary and lummer; hysical 9eology &Earth e$ealed, 10

or se$eral decades after the theory of late Tectonics first was put forth theoutflow of la$a at the ridges was considered to be the prime reason that the

plates on either side were drawn apart. That still is an important factor but todaythere is another aspect that seems to be e$en more influential. The leading edgeof a subducting plate consists of the oldest part of the basaltic outpouring. Thispart has cooled into a dense segment that is being drawn down at the subductiontrench, such as the *arianas Feep. %ts $ery weight helps to force the platedownward, dragging the plate behind it along and away from the ridge. The ridgela$as, while assisting in the plate mo$ement, are emplaced to fill the spaceopened up.

So, how does the late Tectonic *odel tie in with the notion of +ontinental FriftC/r, more to the point, what is the e$idence for driftC The chief proof comes from

#olar +andering. #t the time rocks containing magnetite start to solidify on thecontinent, the magnetic grains are able to mo$e freely in the mush. Theyact liketiny magnets and point to the Earths 'orth pole as does the needle on acompass. #ssuming that the Earths magnetic poles remain constant in position(but not in polarity" o$er $ast time periods & for which there is good e$idence &these grains, aligned in a fied direction by the terrestrial magnetic field, ser$e asmarkers suited to locating the pole at the time they were encased in cooled rock(usually basalts". %f the polarity is determined in rocks of different ages, the

57



positions of the 'orth ole at each age can be plotted, yielding polar wanderingpaths, appearing as follows;

rom Tarbuck and =utgens, The Earth, >rd Ed., 12

This resulting olar Bandering plot is eplained as follows; /n the left diagramare a pair of cur$es made by connecting the geographic location of the pole in'orth #merica and in Europe yielding points at different times & the progression isfrom >22 million years to the resent. 'ote that the two cur$es do not fit on amap that shows todays location of each continent- the cur$es were constructedfrom pole position data ac<uired on 'orth #merica alone and Europe alone. /nthe right diagram, the continents ha$e been pushed back together as they arededuced to ha$e been before the current onset of +ontinental Frift and prior to

breakup of angaea. The two offset cur$es now coincide. This is con$incingproof that at that time the continents were con@oined.

Be ha$e already alluded to the process (actually it is common" of two plateseach bearing a large landmass (up to continental si3e" colliding. %f little oceaniccrust is in$ol$ed at later stages, the continents will collide head on, will probablyweld to each other, and one may o$erride the other, with the result that the nowcombined continents in the collision 3one actually thicken. This has happened inthe case of the %ndian subcontinent heading into the AunderbellyA of +entral #sia,as se<uenced in this diagram. The result is the imalayan *ountains, highest onEarth.

58



This process suggests one means by which continents (which contain moresilica&rich rocks like granites and usually ha$e etensi$e sedimentary rock co$er supracrustal assemblage!" can grow in si3e. The $arious plates in modern times

ha$e not only continents embedded in their upper parts but many smaller features such as island arcs, ruptured continental fragments, and e$en spreadingridges o$erriden ane caught within a plate. Bhen collisions occur, some of thisAflotsamA may subduct but commonly it is sho$ed on and welded to thecontinental margin. These additions are called $erranes and the assemblage of indi$idual terranes that arri$ed at separate times make up what is term AccretedTerranes (also Eotic Terranes- Suspect Terranes- and more formallyTectonostratigraphic Terranes (see Section 18- pages 8&6 ff". The western edgeof 'orth #merica has been built up by a succession of accreted terranes, asindicated in the net figure;

59



rom Skinner and orter, hysical 9eology, 1H8

60



The eastern part of 'orth #merica also has a large number of terranes addedboth before and after the angaea split. There are many terranes making up theiedmont :elt in the #ppalachians. ere is that belt in Qirginia, with each unitbeing an accreted terrane;

Bhole continents may in fact build up largely by terrane accretion, as suggestedin the time map of ro$inces in 'orth #merica appearing earlier on this page.The ancient crystalline rocks that make up the basement of the 'orth #mericancraton (huge continental mass that ser$es as the nucleus for later continentalgrowth", now co$ered by younger hori3onal sedimentary rocks, ha$e been shownfrom penetration by drilling to consist of slices of eotic terranes accreted to thatcraton in its formati$e stages. ere are terranes in the 5ansas basement;

61



Thus, as has been alluded to in the paragraphs abo$e, for emphasis we repeatthe modern day $iew of how orogenic mountains are built by folding, faulting, anduplift that are the conse<uence of two mechanisms; 1" the deformation thatoccurs within the rocks caught in the basins and shelfs ad@acent to land massesunder which oceanic crust is being subducted- and 0" the smashing of rock

masses in one crustal segment against another during terrane accretion. Thereare other ways to make mountains, such as through block faulting where thecrust is uparched and stretched (the :asin and ange of 'e$ada" and by thepiling up of la$a at $olcanoes. Furing and after a mountain system is de$eloped itcan be further modified by re@u$enation through isostatic ad@ustment (balancingout differences in gra$itational attraction" and by erosion by streams and glaciers.

To further illustrate some of these ideas behind the tectonic history of mountainsystems, we will look briefly at the #ppalachians & the orogenic comple that ledto early ideas of mountain&building in the 1H22s. irst, the setting; ere are themain structural (and correlated landforms" subdi$ision of todays #ppalachian

*ountains in the eastern D.S.

The iedmont is mostly metamorphic and igneous rocks (including terranes" thatwere heated up both prior to the final collision (end of ermian" and during that

@uncture. They continue to the east but are co$ered by younger coastal plainssedimentary rocks. The :lue idge is an assemblage of older rocks that resisterosion and thus rise topographically abo$e the iedmont. The Qalley and idgeunit is a se<uence of folded anticlines and synclines deformed during the Taconic(/rdo$ician", #cadian (Fe$onian", and #lleghenian (ermian" orogenic e$ents(perhaps related to terrane accretion". The #ppalachian lateau is a thickse<uence of trans&aleo3oic sedimentary rocks that filled basins against the'orth #merican protocontinental margin, which was not crumpled by the main

62



folding but was uplifted (then, and by re@u$enation se$eral times since". The'orthern #ppalachian unit is mostly metamorphic)igneous rocks to some etentcorrelati$e with the iedmont. The #ppalachians continue northward into 'o$aScotia and thence across the since opened #tlantic /cean into %reland)westernEngland)Scotland)'orway. To their southwest, these mountains are now buried

by the *ississippi Embayment sedimentary rocks but appear again in #rkansas)/klahoma and westward to reappear in *eico.

%n this fi$e panel illustration, the ma@or steps and e$ents in #ppalachian*ountains history are shown from recambrian (top" to the present (bottom"- the%apetus /cean is ancestral to the #tlantic.

rom Skinner R orter, The Fynamic Earth, 0nd Ed., 17

This se<uence is likely; 1" %n =ate recambrian, a plate east of the 'orth #merican block (already eisting for a long time" subducted, causing am island

63



arc (welded on as a terrane" and a back arc depositional basin- 0" %n +ambriantimes, a rupture near the margin produced a second subduction 3one pointing ina direction opposing the first- $olcanism and deposition continued- >" %n the/rdo$ician and again in the Fe$onian, more boundary&subduction, with attendantterrane accretion, occurred producing the Taconic and #cadian mountains &

precursors to the present- 4" #s the main westward mo$ement of the #fricanplate continued to subduct crust and embedded rocks under and onto 'orth #merica, the #frican continent itself approached- the %apetus /cean between thetwo continents progressi$ely closed- 7" in time near the end of the aleo3oic the

#frican continent crashed against 'orth #merica, closing the %apetus, but byTriassic times the two continents split and the #tlantic /cean opened- there nolonger is an acti$e subducti$e 3one net to either continent. This runningdescription helps to demonstrate that plate tectonic action can lead to somecomplicated se<uences of e$ents. #n informati$e re$iew of the growth of thenorthern #ppalachians, including terrane accretion, is worth a $isit to this website.

The ancestral #ppalachians may ha$e been as high as the imalayas andcertainly the #lps. The mountains ha$e since been worn down by erosion. Thepresent day #ppalachians are re@u$enated, as ad@ustments in the crust under changing gra$itational forces owing to remo$al of mass ha$e caused them to beuplifted. The current Qalley and idge part of the #ppalachians owes its form &ridges of nearly the same heights separated by $alleys & to differential erosionwith the ridges usually made up of sandstones and the $alleys shale and)or carbonates. (See page 6&> for a further re$iew of the #ppalachians."

,olcanism

Be ha$e touched upon $olcanoes on these two 9eology tutorial pages. They arethe most spectacular of the ma@or geologic pages (although earth<uakes can bemore detructi$e". ere we will consider se$eral of their general aspects (sometypes of $olcanoes, especially as seen from space, are eamined on page 18&>".

Bhen one thinks of a A$olcanoA, this photo is typical of what comes to mind;

64

http://www.jamestown-ri.info/northern_appalachians.htm






This $olcano, *t. ainier in Bashington state, is a classic strato$olcano, whosestructure is shown here;

# $olcano, then, is a surficial structure that is built up of melted rock that reachesthe surface as la$a, which has one or more features that connect to a magmachamber in the crust, or possibly the upper mantle. # series of eruptions (usuallymany" lead to a gradual buildup of the structure as the component material pilesup as ash or as outflows of molten rock. Stratocones generally are composed of la$as that ha$e high to intermediate silica content.

There is a second ma@or type of $olcanic structure, the shield $olcano, whoseslopes are gentler (7 to 17 degrees". *auna =oa in awaii is an eample;

65



There are other, smaller $olcanic types and landforms (again, see page 18&>".:ut for this tutorial we will place $olcanoes in their tectonic setting. These broadclasses are set forth; 1" those that occur within a continent in a rift 3one wherethe continent is splitting apart- 0" those found along spreading ridges of upwellingmagma- >" those located abo$e a subduction 3one- 4" those produced abo$e anacti$e hot spot (a column of upwelling magma- and 7" those that appear to beisolated from main 3ones of tectonic and)or magmatic acti$ity.

This net map shows the distribution of the fi$e classes;

+lass 1 is illustrated by the East #frican ift Qalley, where an arm of a triple @unction (three 3ones of upwelling magma roughly 102 degrees apart" is breakingthe ontinent to the east apart from the main mass of #frica. +onsider these twoillustrations;

66



The #tlantic idge is a good eample of $olcanoes along a spreading 3one. Thenumber of $olcanoes is rather small, and some are underwater (submarine$olcanoes". There are clusters of $olcanoes in the +anary %slands, the #3ores,and %celand. This is a photo of %celandic $olcanoes;

67



=ong lines of $olcanoes, or chains, are typical of those found along subduction3ones (+lass >". This (rather busy" map of %ndonesian $olcanoes, on the up plateside of a $ast subduction 3one, and a photo of a line of $olcanoes from space,show this class;

68



The awaiian %slands are the most fre<uently cited eample of +lass 4 & hot spot$olcanoes. (Gellowstone ark sit on top of a hot spot." #nother, less familiar,eample is +he@u %sland, off the coast of 5orea in the Gellow Sea;

Be will not show any eamples of the +lass 7 isolated $olcanoes. The Keme3mountains in 'ew *eico fall in this group.

69



Closing Remarks

Be ha$e said little about how the Earth was formed as a planet and de$elopedduring its first three billion years. or that, go to page 1&0a.

So there you ha$e it; %n these two pages some of the rudiments of 9eology &some but not all of its principal ideas & ha$e been re$iewed to gi$e you a workingbackground to appreciate material in this and other Sections. To learn more &hunt through the %nternet or take a course in college. #nd, a plug gi$en here toreach any who, like the writer ('*S", may aspire to 9eology as a career; % pointwith the following photo to a AtrademarkA of this profession & the @oy of beingoutdoors doing field work , as illustrated in this trip in 166 which % participated induring an /regon +onference on Qolcanism;


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http://rst.gsfc.nasa.gov/Sect19/Sect19_2a.html




I$*%#+!*$ * h G**1!+& F&# *3 h M**$

Tue, 02/06/2007 - 13:35

A*# h &#h*

Dan Luna

I$*%#+!*$

The Moon is the only natural satellite o the !arth an" or#e" at a$out the sa#e ti#e,o%er our an" a hal $illion years a&o, $ut has not e%ol%e" in the sa#e 'ay( La)*in& anat#os+here, 'ater an" lie, an" ha%in& )oole" #ore ra+i"ly "ue to its s#aller sie, #u)h

o the sura)e has not $een )han&e" si&nii)antly or $illions o years(

This arti)le +ro%i"es a $rie intro"u)tion to the ty+es o &eolo&i)al eature to $e oun" onthe Moon, to assist in any )o#+arison 'ith other +lanets an" to hel+ the rea"er "e)i"e'hether there are any to+i)s they 'oul" li*e to in%esti&ate urther(

L&1 +& 3&#

The lar&est eatures %isi$le are the $ri&ht, hea%ily )ratere" areas *no'n as the terraeLatin or .lan". an" the "ar*, relati%ely s#ooth an" li&htly )ratere" areas )alle" the

#aria Latin or .sea., sin&ular .#are.( These are sho'n in i&ure 1(

71



Figure 1: The Moon seen from Apollo 1, clearly showing the terre and mares.

I'&+ C&

#+a)t )raters are the "o#inant lan"or#, an" s+an the entire ran&e o sies ro#ra)tions o #illi#etres to thousan"s o *ilo#etres in "ia#eter( n in"i%i"ual )rater 'illsho' a nu#$er o "ierent "e+osits an" )hara)teristi)s "e+en"in& on its sie an" le%el o erosion( These in)lu"e ee)te" $lo)*s, raise" ri#s, hu##o)*s, i#+a)t #elt, 'all slu#+s,terra)es, lo's, )hannels, loor ra)tures, )entral +ea*s, +ea* rin&s, rays, se)on"ary)raters an" )rater )hains( The s#all )rater $elo' i&( 2 sho's as a $o'l 'ith a shar+ri# )rest, $ri&ht )ontinuous ee)ta an" $ri&ht rays(

72



Figure 2: 3 km diameter crater

#ooth #aterial, +ossi$ly i#+a)t #elt, has lo'e" a'ay ro# the ri# )rest o this lar&er)rater i&( 3(

73



Figure 3: Flows on rim of 14 km crater

74



e)on"ary )raters, +ro"u)e" $y ee)ta ro# lar&er +ri#ary i#+a)t )raters, oten or#)hains or )lusters i&( 4(

Figure 4: Chain of secondary craters

75



The i#+a)t )raters $elo', or#e" on a #are sura)e, sho' internal slu#+ terra)es an")on)entri) arran&e#ents o "ierent ty+es o ee)ta "e+osit i&( 5(

Figure 5: 2 km and 1! km craters with the larger crater showing sl"mping inside thecrater.

76



raters #ay $e #o"iie" ater their initial or#ation( n this )ase, u+lit o the loor othis 200 *# )rater i&( 6 a++ears to ha%e resulte" in )ra)*s an" issures(

Figure 6: Fiss"red crater floor

77



s they &et lar&er, )raters "e%elo+ )entral +ea*s, rin&s an" e%entually #ulti+le rin&s, as inthe )ase o the rientale asin $elo' i&( 7(

Figure 7: #rientale $asin

V*+&$!+ &$% T+*$!+ F&#

The s#ooth #are +lains are or#e" $y the illin& o "e+ressions, +arti)ularly lar&e $asins, $y $asalti) la%a that has $een eru+te" ro# "ee+ 'ithin the Moon( ota$le eaturesin)lu"e 'rin*le ri"&es, %ol)ani) "o#es an" sinuous rilles( Te)toni) eatures in)lu"e aultsan" &ra$en ault $oun"e" tren)hes( n ea#+le o la%a lo's is sho'n $elo' i&( 8,'ith lo's eten"in& ro# $otto# let to to+ ri&ht, an" 'rin*le ri"&es )rossin& in the)entre(

78



Figure 8: %a&a flows and wrinkle ridges

79



rin*le ri"&es are $elie%e" to $e )ause" $y )o#+ressional or)es as the "ense la%a illin&a $asin settles i&( 9(

Figure 9: Close "p of wrinkle ridge

80



The 'in"in& )hannels $elo' i&( 10 ha%e +ro$a$ly $een )reate" $y lo'in& la%a,althou&h su""en )han&es in "ire)tion #ay $e inluen)e" $y aults(

Figure 10: 'in"o"s rille. The (right crater is 43 km wide.

81



n this eature i&( 11 a hi&hly 'in"in& )hannel is )ontaine" 'ithin a $roa"er %alley,itsel )ut into a la%a +lain(

Figure 11: )ested channels

82



;ere the )rater i&( 12, 100*# in "ia#eter, has $een ille" 'ith la%a in 'hi)h a sinuousrille has "e%elo+e"(

Figure 12: *ille within flooded crater

83



The linear rilles, or &ra$en, sho'n $elo' i&( 13 )uttin& throu&h $oth the #are sura)ean" the )rater, are a$out one *ilo#etre 'i"e( These are thou&ht to $e the result o tensional or)es stret)hin& the sura)e an" are #ost )o##on near the $or"ers o )ir)ular #aria(

Figure 13: +ra(en c"tting crater

84



This +hoto i&( 14 sho's a$out 120 *# o a 300 *# rille, another ault trou&h or &ra$en)ause" $y sin*in& $et'een t'o +arallel aults(

Figure 14: %inear rille

C*$+#!*$

The #ain eatures o the Moon are i#+a)t )raters s+annin& the ull ran&e o sies an"lar&e s)ale $asalti) la%a lo's 'ith asso)iate" )hannels an" aultin&( The %ery slo' rateo erosion, li#ite" lateral #o%e#ent o "e$ris, an" la)* o sura)e )o%er su)h as%e&etation ha%e +reser%e" an" let %isi$le lan"or#s "atin& $a)* $illions o years an"thus #a*e the Moon %ery useul or stu"yin& the early history o the olar yste#(

R3$+

Masurs*y, ;arol"< olton, =( ( > !l-a, arou* e"s(, A** *4 h M**$5 A

V!6 3*' O!, ?-362, 1978( nline @ersion

F#h R&%!$1

The ollo'in& a""itional $oo*s also )ontain nu#erous +hoto&ra+hs 'ith e+lanatory)o##ents $y lunar &eolo&ists( lthou&h out o +rint, use" )o+ies #ay $e a%aila$le(

85

http://www.hq.nasa.gov/office/pao/History/SP-362/cover.htm




Aosos*y, L(B(< !l-a, arou*, Th M**$ & V!6% 2 L#$& O!, ?-200, 1970(

Lo'#an, ?aul D, L#$& P&$*&'&5 A Ph**1&h!+ G#!% * h G**12 *3 h

M**$, eltlu&$il" Ceinhol" ( Muller, 1969(

Ph** S*#+

ll +hotos ori&inate ro# , #ainly +ollo $ut so#e ro# the earlier Lunar r$iters(The ollo'in& online )olle)tions 'ere use":

+ollo %er The Moon: @ie' ro# r$it

Lunar an" ?lanetary nstitute Lunar tlases

= Lunar r$iter Di&itiation ?roe)t

86


http://www.lpi.usra.edu/resources/lunar_atlases/

http://astrogeology.usgs.gov/Projects/LunarOrbiterDigitization/


http://www.lpi.usra.edu/resources/lunar_atlases/

http://astrogeology.usgs.gov/Projects/LunarOrbiterDigitization/



$he second Section concentrates on a%%lications of remote sensing togeological studies' # list of %rinci%al uses egins this %age' S%ecial attention isgiven to ways in which remote sensing (es%ecially through image classification)can aid in making geologic ma%s' $he notion of *formation* is discussed and reasons given as to why this standard geologic ma% unit cannot e recogni+ed

as such in imagery alone' One of the %itfalls of making these ma%s solely fromimagery ! namely, the %resence of soil and-or vegetation cover ! is mentioned'Some ty%ical s%ectral signatures of different rock ty%es are dis%layed'

-.T$ T. $)CAT.RS0 T%S SE+T%/', % B/5EF T/D9 %' %TSE'T%ETG, +#' #=*/ST :E TE#TEF #S # .&/&COURSE %' TED'F#*E'T#=S / 9E/=/9G. *any readers of the Tutorial and particularlySections 0, 7, 18, and 1, will find the geological concepts and underlyingprinciples unfamiliar or e$en unknown to them. To assist these indi$iduals inbuilding a <uick background, a primer or re$iew of the essential ideas of 9eology

is offered as an added page, which you can access by clicking here. # similar opportunity is pro$ided in Section 14 dealing with rinciples of *eteorology.Sections 1 and 02 are likewise e<ui$alents of short courses in lanetology and

#stronomy)+osmology.

G$.L.GIC A##LICATI.-S0

STRATIGRA#H1 A-) STRCTR$

General Background

The synoptic character of =andsat and other large&area co$erage satellite remotesensors is pro$ing especially fa$orable in geologic mapping and other geologicapplications. =and co$er)use, agriculture, urban monitoring, and similar non&geologic acti$ities related to human endea$ors for the most part relate to arealco$erage at smaller scales. 9eologic phenomena typically are spread o$er wider scenes, so that the ability to see the Aregional pictureA is a powerful attribute of space imagery. This perception is supported by the discussion of landformsanalysis that makes up most of Section 18.

This $iew is somewhat tempered by the AinterferenceA of $egetati$e co$er in

trying to single out geologic features. #erial photography and space imagerywork especially well on geologic sub@ects when the scenes they portray areminimally co$ered with $egetation. Early spring pictures are usually optimal(before leafing". #lso, best results obtain when rocks are eposed (outcrop", areco$ered with little soil or are bare, and are not buried by allu$ial deposits. Thebest images seen in this Section are in the western Dnited States and aridregions elsewhere in the world.

87





9eologists ha$e used aerial photographs for decades to ser$e as databasesfrom which they can do the following;

1. ick out rock units (stratigraphy"

0. Study the epression and modes of the origin of landforms (geomorphology"

>. Fetermine the structural arrangements of disturbed strata (folds and faults"

4. E$aluate dynamic changes from natural e$ents (e.g., floods- $olcaniceruptions"

7. Seek surface clues (such as alteration and other signs of minerali3ation" tosubsurface deposits of ore minerals, oil and gas, and groundwater.

6. unction as a $isual base on which a geologic map is drawn either directly or

on a transparent o$erlay.

Bith the ad$ent of space imagery, geoscientists now can etend that use in threeimportant ways;

1" The ad$antage of large area or synoptic co$erage allows them to eamine insingle scenes (or in mosaics" the geological portrayal of Earth on a regional basis

0" The ability to analy3e multispectral bands (especially hyperspectral data sets"<uantitati$ely in terms of numbers (F's" permits them to apply special computer processing routines to discern and enhance certain compositional properties of

Earth materials

>" The capability of merging different types of remote sensing products (e.g.,reflectance images with radar or with thermal imagery" or combining these withtopographic ele$ation data and with other kinds of information bases (e.g.,thematic maps- geophysical measurements and chemical sampling sur$eys"enables new solutions to determining interrelations among $arious naturalproperties of earth phenomena.

Bhile these new space&dri$en approaches ha$e not yet re$olutioni3ed the waysin which geoscientists conduct their field studies, they ha$e pro$en to be

indispensable techni<ues for impro$ing the geologic mapping process andcarrying out practical eploration for mineral and energy resources on a grandscale.

The $ery first practical use of ETS&1 (=andsat&1" imagery in any discipline wasthe drawing by Fr. aul F. =owman, Kr, of a geologic structures mapsuperimposed on the first color composite image, based in part on already knownfield information and in part on his interpretation of this scene. e is a geologist

88



at 9oddard Space light +enter, and an epert on space photography (heprepared Section 10 on #stronaut %magery in this Tutorial". The image was of thecentral +alifornia coast around *onterey :ay, ac<uired > days after launch.

This map confirmed predictions from his studies of astronauts photos that

=andsat would be an efficient tool for recogni3ing faults and other knownstructural trends in small&scale imagery. %n spite of lower resolutions, theseimages ecel in portraying regional geologic settings and are easily enhanced bydigital processing.

Be now consider se$eral eamples of geologic applications using these newapproaches. Be concentrate initially on how =andsat Thematic *apper (T*"data for a local region in Dtah are manipulated to identify different rock types,map them o$er a large area using super$ised classification, and correlate their spatial patterns with independent information on their structural arrangement.'et, our focus changes to eamination of geologic structures, particularly

lineaments, as displayed in regional settings in the D.S., +anada, and #frica.Then, in Section 7, we will look at how space&ac<uired data fit into currentmethods of eploring for mineral and hydrocarbon deposits by considering acase study of a minerali3ed 3one in Dtah and at a large&area =andsat scene in/klahoma. %n Section 18, we will return to a geologic theme by eamininglandforms at regional scales, (so&called *ega&geomorphology", as a primeeample in considering how remote sensing is used in basic science studies.

89



*ost geologic maps are also stratigraphic maps, that is, they record the locationand identities of se<uences of rock types according to their relati$e ages. Thefundamental rock unit is the *ormation (abbre$iated as m or fm", defined simplyas a distinct mappable set of related rocks (usually sedimentary" that has aspecific geographic distribution. # formation typically is characteri3ed by one or

two dominant types of rock materials.

The term AformationA is most commonly associated with strata, namely layers of sediments that ha$e hardened into sedimentary rocks. Dnder most conditions,sediments are laid down in hori3ontal or nearly so layers on sea floors, lakebottoms, and transiently in ri$er beds. ere is a typical set of sedimentary layerseposed in a road cut (note that the layers ha$e been cut and slightly offset by abreak which is termed a AfaultA";

%f we see sedimentary rocks inclined at more than a few degrees from thehori3ontal, we should suspect that these are in$ol$ed in displacements from their original hori3ontal state by forces (tectonic" that cause the rocks to bend andcur$e (folds" or break (faults". ere is a roadcut along a *aryland highway that ispassing through the fold belt of the #ppalachians.

90



#s we shall see later in this Section, inclined layers can produce cur$edstructures called anticlines (uparched" and synclines (downarched", ere is aneample of the latter;

#ny gi$en formation is de$eloped and emplaced o$er some finite span of geologic time. Be can approimate its age by the fossils (e$idence of past life"that were incorporated within the soft layers (which become strata or beds"during the time in which these life forms eisted. #ge dating by determining theamounts of radioacti$e elements and their decay&daughter products can usuallyproduce e$en more accurate age estimates. #nother, less precise, approach tofiing the age (span" of a rock unit is to note its position in the se<uence of other rock units, some of whose ages are independently known. Be can correlate the

91



units with e<ui$alent ones mapped elsewhere that ha$e had their ages workedout. This method tends to bracket the time in which the sedimentary formationwas deposited but erosional influences may lead to uncertainties. Theassociation of sedimentary layers with specific time inter$als constitutes the fieldof stratigra%hy . %gneous and metamorphic rocks also ha$e time significance and

are treated as rock units on geologic maps (which show all stratigraphic andcrystalline units in a legend".

emote&sensing displays, whether they are aerial photos, space&ac<uiredimages, or classification maps, show the surface distribution of the multipleformations usually present and, under appropriate conditions, the type(s" of rocksin the formations. The formations show patterns that depend on their proimity tothe surface, their etent o$er the sur$eyed area, their relati$e thicknesses, their structural attitude (hori3ontal or inclined layers", and their degree of erosion.Eperienced geologists can recogni3e some rock types @ust by their appearancein the photo)image. They identify others types from their spectral signatures.

/$er the spectral range co$ered by the =andsat T* bands, the types and ages of rocks show distinct $ariations at specific wa$elengths. This is e$ident in thefollowing spectral plots showing laboratory&determined cur$es obtained by areflectance spectrometer for a group of di$erse sedimentary rocks (collected fromtheir field formations named from a geographic locality near where thefromationas unit was first described" from Byoming;

234 %rom these spectra5 predict the general color o* these *our rock units0-iorara %m& Chug'ater %m& %rontier %m& Thermopolis %m6 A-S+$R

92

http://rst.gsfc.nasa.gov/Sect2/answers.html#2-1




232; +hat spectrally distinguishes the Mo'ry %m *rom the Thermopolis %m7oth dark in the *ield8& the 9elm %m *rom the +hite Ri(er Conglomerate:A-S+$R

Se$eral of these spectral signatures are composite, in that more than one

mineral substance is present. Spectra of indi$idual minerals can be <uitedifferent, as shown in the net illustration;

The 'ear&% wa$elength inter$al from 0.2 to 0.4 m is especially sensiti$e toabsorption of radiation- note that all four minerals share a negati$e peak (trough"around 0.>0 m. :ut a word of caution; there are se$eral thousand mineralspecies known from Earth. The spectra of many of these can be similar, makingfield and e$en laboratory distinction of @ust what mineral species is being lookedat difficult to assess (J&ray diffraction patterns are usually better identifiers".Bhen remote sensing is in$ol$ed in onsite sur$eys, knowledge beforehand of the

particular minerals likely in the sensed scene is usually a benefit. Thus, when anarea is being sur$eyed for specific mineral content (as in eploration for oreminerals- Section 7", this information aids in identifying the mineral species beingmapped. This is also true for rock types- whene$er possible, field spectra such asshown abo$e for Byoming formations are gathered as 9round Truth (Section 1>"so that their diagnostic characteristics can be used to calibrate the imageanalysis (as an eample, referring to the rock spectra abo$e, the a$eragedreflectances of the 6 non&thermal T* bands can be calculated for, say, the*uddy Sandstone- this knowledge could then be fed into a computer classification as a discriminator function which looks for all piels with similar multiband $alues".

# common way of mapping formation distribution is to rely on training sites atlocations within the photo)image. 9eologists identify the rocks by consulting areamaps or by $isiting specific sites in the field. They then etrapolate the rocksappearance photographically or by their spectral properties across the photo or image to locate the units in the areas beyond the training sites (in effect, thesuper$ised classification approach".

93





%n doing geologic mapping from imagery, we know that formations are notnecessarily eposed e$erywhere. %nstead they may be co$ered with soil or $egetation. %n drawing a map, a geologist learns to etrapolate surfaceeposures to underneath co$ered areas, making logical deductions as to whichhidden units are likely to occur below the surface. %n working with imagery alone,

these deductions may pro$e difficult and are a source of potential error. #lso,rock ages are not directly determined from spectral data & only material types aredetermined, so that identifying a particular formation re<uires some independentinformation (knowledge of a regions rock types and their se<uence".

%n eceptional instances, such as those to be shown on the net three pages,when geologic strata are turned on their side (from folding- discussed on page 0&7" so that the successi$e geologic units are $isible as a se<uence, the changeswithin and between each discrete unit can be measured in terms of somespectral property, as for eample, $ariations in the reflectance of a gi$en band, or a ratio of bands. Bhen plotted as shown below the result are tracings that

resemble (analogously" those made from well logging of such properties aselectric resisti$ity, permeability, magnetic intensity and other geophysicalparameters. ere are two figures, the top showing the succession of sedimentarystrata eposed along the +asper #rch in central Byoming- the bottom beingreflectance AlogsA deri$ed from spectral tra$erses along one of the lines in theupper image;

94



%n the lower diagram, the bottom unit is the ermian hosphoria ormation,etending upward from the Triassic +hugwater ormation to the rontier sandstone (+retaceous" at the top. /n the right the left tracing is of T* :and >(red", with 2L reflectance on the right base etending to 82L on the left, and theright tracing, for :and 1, goes from 2L on the left to 72L on the right.

:efore looking at some specific eamples of the use of space imagery for geologic structure analysis, this is a good point to introduce one particular ad$antage of ha$ing space obser$ing systems that can repetiti$ely co$er thesame large regions o$er the four seasons. Two =andsat images appear below;

one taken during the southern Binter in South #frica- the other during the heightof Spring. The area includes Kohannesburg, some of the gold mines in theBitwatersrand district, and the ilanesburg pluton (near the top". %n thewintertime, some of the underlying rock units fail to show distinctly because theentire scene has its $egetation (mostly grasslands" dormant. :ut with plantreawakening in Spring, different units ha$e different $egetation types and these$ariably modify the colors displayed, thus re$ealing the more comple structuresin the region.

95



This geobotanical phenomenon (the differential distribution of $arious plant types

as a function of soils de$eloped on different rock types" is sometimes used as amapping or prospecting de$ice (eample- the element Selenium is associatedwith Dranium- certain plants thri$e on Selenium enrichment and are thusindicators of subsurface Dranium enrichment".


96



A$ I$*%#+!*$ * G**12

Thu, 01/04/2007 - 21:28

A*# h &#h*

Bon ni%ersity o !"in$ur&h

I$*%#+!*$

=eolo&y is, $roa"ly s+ea*in&, the stu"y o the !arth( t is s+lit into se%eral "is)i+lines,in)lu"in&: ?etrolo&y the stu"y o ro)*s, =eo+hysi)s the stu"y o the !arth usin& +hysi)s, ?alaeontolo&y the stu"y o ossils an" Mineralo&y the stu"y o #inerals( The#ain ai# o &eolo&y is to un"erstan" ho' the !arth 'or*s< ho' #ountains are $uilt, ho'the o)eans or#, 'hat "inosaurs loo*e" li*e( The !arth is )onstantly )han&in&, $othinsi"e an" outsi"e( The at#os+here an" 'ater ero"e an" 'eather ro)*s< )ollision o )ontinents $uil" #ountain ran&es< an" ne' )rust or#s at the #i"-o)ean ri"&es( ;o' "othese +ro)esses relate to ea)h other, an" )an 'e )o#e u+ 'ith a #o"el to e+lain thesethin&sE n)e 'e ha%e su)h a #o"el, the a++li)ations o &eolo&y $e)o#e #u)h si#+ler(++li)ations in)lu"e the sear)h or oil, &as, 'ater an" #inerals< en%iron#ental stu"ies<

re)onstru)tin& the +ast en%iron#ents o the !arth, 'hi)h hel+s us 'ith +re"i)tin& theuture(

=eolo&y has $een re%olutionise" $y the intro"u)tion o the theory o plate tectonics( Thistheory e+lains a &reat "eal o the thin&s 'e see on the !arthFs sura)e an" hel+s a &reat"eal 'hen tryin& to it the +ie)es to&ether( t is +late te)toni)s 'hi)h +ro%i"es a #o"el in'hi)h to +ut the "etails(

The !arth has a layere" inner stru)ture i&ure 1(

97



Figure 1: The interior str"ct"re of the arth, with a close "p of thelithosphere-asthenosphere (o"ndary. *edrawn from l"mmer / Mc+eary, 1!!.

The !arth is #a"e o three #ain layers: the lithos+here, the #antle an" the )ore( This ares+lit urther, $ut this is $eyon" the s)o+e o this tutorial( The lithos+here is "i%i"e" into aseries o +lates 'hi)h #o%e aroun" the sura)e o the !arth as "i)tate" $y +late te)toni)theory( t is the lithos+here 'hi)h is #a"e o ro)* as 'e see it e%ery"ay(

M!$&

Minerals are the )onstituents o ro)*s, an" hen)e o the !arth at least the )rust an"#antle( Minerals )onsist o #ole)ules an" ato#s arran&e" in an or"erly #anner an" arethereore )lassiie" as crystalline soli"s( There are hun"re"s, i not thousan"s, o "ierent#inerals( There are "oens o &rou+s o #inerals, ea)h 'ith itFs o'n ty+e o stru)ture(!%ery #ineral is #a"e o ato#s, ust li*e e%ery other #aterial( to#s )onsist o +rotonsan" neutrons at the n"cle"s o the ato#, 'ith ele)trons or$itin& aroun" it i&ure 2(

98



Figure 2: The str"ct"re of the atom. The yellow spheres are electrons, the (l"e ne"trons,the red protons. *edrawn from l"mmer / Mc+eary, 1!!.

The +rotons re" ha%e a +ositi%e )har&e, neutrons $lue ha%e no )har&e an" ele)tronsyello' ha%e a ne&ati%e )har&e( Due to the arran&e#ent o these three )onstituent +artsato#s "o not ha%e any o%erall )har&e( The sharin& o ele)trons $et'een ato#s or#sions, 'hi)h are ato#s 'hi)h ha%e so#e )har&e( onne)tions $et'een ions #a*es

#ole)ules( The #ole)ules are then arran&e" in an or"erly ashion to or# the #inerali&ure 3( Most o the )o##on #inerals in ro)*s are sili)ates, 'hi)h in)lu"es Guart,el"s+ar, ?yroene an" ;orn$len"e(

Figure 3: A silica tetrahedra. *edrawn from l"mmer / Mc+eary, 1!!.

ili)ates )onsist o sili)a an" oy&en 'ith so#e other ions( ll sili)ate #inerals ha%e astru)ture $ase" on the sili)a tetrahe"ra, an arran&e#ent o 1 sili)a ato# an" 4 oy&enato#s i&ure 3( The )he#i)al or#ula or this is i4( The #ain &rou+s o #inerals are:sin&le, )hains, "ou$le )hains, sheets or ra#e'or* arran&e#ents o these tetrahe"ra( Most

soli" #aterials are )rystalline - that is the ato#s #a*in& this soli" are arran&e" in are&ular re+eatin& or"er( the #aterials is not )rystalline, then it is a#or+hous( na#or+hous soli" is &lass, 'hi)h is a sili)ate liHui" .roen. soli"(

&eolo&i)al #ineral is "eine" to $e:

1( )rystalline soli"

99



2( aturally o))urrin&

3( nor&ani)

4( Deinite )he#i)al )o#+osition

Minerals ha%e se%eral i#+ortant +ro+erties 'hi)h hel+ i"entiy the#:

• olour - usually not a &oo" in"i)ator, as it "e+en"s on the ea)t )he#istry(• trea* - 'hen &roun" u+ the #ineral is al'ays the sa#e )olour - itFs strea*(• Luster - ho' li&ht rele)ts ro# the #ineral, e(& #etalli) #inerals ha%e a #etalli)

luster(• ;ar"ness - relia$le test( ;arness is )o#+are" to MohFs har"ness s)ale(• ;a$it - the sha+e o the )rystals, "e+en"s on the a#ount o &ro'th(• ra)ture - ho' the #ineral $rea*s 'hen not alon& a )lea%a&e +lane(• lea%a&e - ho' the )rystal $rea*s u+( lea%a&e +lanes are inherent +lanes o

'ea*ness(

Wh& ! & R*+78

hat see#s to $e a si#+le Huestion is a)tually %ery )o#+li)ate"( ll ro)*s are ulti#ately#a"e o #inerals an" there are three #ain ty+es o ro)*s:

• &neous• Meta#or+hi)• e"i#entary

These are then su$"i%i"e" into hun"re"s o "ierent ty+es o ro)*s(

e"i#entary ro)*s are #a"e o ra&#ents o other ro)*s< i&neous, #eta#or+hi) or se"i#entary( They are #a"e 'hen an ol"er ro)* ero"es or 'eathers to +ro"u)e se"i#ent,or instan)e san" on a $ea)h( The se"i#ent is then )o#+a)te" an" )e#ente" to&ether to +ro"u)e a ro)*( e"i#entary ro)*s )an also )ontain in"i%i"ual &rains o #inerals 'hi)hha%e $een ero"e" out o ol"er ro)*s(

&neous ro)*s are or#e" ro# the )oolin& o #a&#a - #olten ro)*( They are the ro)*sthat or# ro# %ol)anoes(

Meta#or+hi) ro)*s are a result o heat an" +ressure on +re-eistin& ro)*s 'hi)h un"er&o)han&es in the soli" state( o #eltin& o))urs( They are asso)iate" 'ith #ountain $eltsan" aroun" i&neous intrusions(

100



Th R*+7 C2+

The ro)* )y)le sho's ho' the three ro)* ty+es relate to ea)h other i&ure 4(

Figure 4: The rock cycle. *edrawn from l"mmer / Mc+eary, 1!!.

The our +ro)esses: 'eatherin&, )rystalliation, lithii)ation an" #eta#or+his# are thelin*s $et'een the ro)* ty+es, se"i#ent an" #a&#a #olten ro)*( eatherin& is the&ra"ual 'earin& "o'n o all ro)* ty+es on)e they are e+ose" at the sura)e(rystalliation is the )oolin& o #a&#a to or# an i&neous ro)*( Lithii)ation is the

transor#ation o loose se"i#ent into a ro)* $y a sli&ht heatin& an"/or )e#entation(Meta#or+his# o))urs 'hen a ro)* is su$e)te" to heat an" +ressure, transor#in& a ro)*, $ut not #eltin& it( This )an o))ur on any ro)*, e%en a #eta#or+hi) ro)*(

C*$+#!*$

=eolo&y is the stu"y o the !arth( The un"e#ental theory 'hi)h un"er+ins &eolo&y isthe theory o +late te)toni)s( Co)*s are "i%i"e" into three $asi) &rou+s: i&neous ro)*s,'hi)h are or#e" ro# )oolin& o #olten ro)*s< #eta#or+hi) ro)*s, 'hi)h are ro)*s thatha%e $een altere" $y heat an" +ressure< an" se"i#entary ro)*s, 'hi)h are ro)*s or#e"ro# )lasts o ol"er ro)*s or )he#i)ally +re)i+itate"( ll ro)*s are or#e" o #inerals,'hi)h are re&ular arran&e#ents o #ole)ules into )rystals( The ro)*s are lin*e" to&ether $y the ro)*s )y)le(

R3$+

( ?lu##er an" D( M)=eary, 1997( Physical Geology. $"y 0t

101

http://www.amazon.co.uk/exec/obidos/ASIN/0071153918/geologyrocks-21




A$ I$*%#+!*$ * S#+#& G**12

Thu, 01/04/2007 - 21:49

A*# h &#h*


I$*%#+!*$

tru)tural &eolo&y is the stu"y o the eatures or#e" $y &eolo&i)al +ro)esses( eaturesin)lu"e aults, ol"s an" "i++in& strata( =eolo&ists )an 'or* out the or"er o e%ents an"see 'hi)h e%ents are relate" $y ta*in& airly si#+le #easure#ents an" usin& si#+le#etho"s(

M&#'$ &$% T+h$!9#

The #ost o$%ious thin& to "o 'hen tryin& to "e)i+her the stru)tural history o aor#ation is to "es)ri$e it( ne 'ay o "oin& this is to #easure the dip an" strike( The "i+is the a#ount a $e" o ro)* is ti++e" ro# the horiontal( The stri*e is the "ire)tion 'hi)h

is ninety "e&rees ro# the "i+, i(e( alon& the horiontal line on the $e"( The stri*e )an $ein t'o "ire)tions, hen)e the "i+ )oul" $e in one o t'o "ire)tions also( There is a)on%ention or the stri*e to $e the in the "ire)tion you are a)in& i the ro)*s are "i++in&to your ri&ht( o#e &eolo&ists +reer to #easure the "i+ "ire)tion, rather than stri*e, as itis sli&htly si#+ler( ;o'e%er, all #a+s use "i+ an" stri*e, not "i+ "ire)tion(

This is )o#+li)ate" sli&htly $y apparent dip( This is "ue to the a)t that you are notal'ays loo*in& e"&e on +er+en"i)ular to the $e" you are #easurin&( you are loo*in&at a $e" at a sli&ht an&le, then you see the a++arent "i+( The tr"e "i+ 'ill $e &reater thanthe a++arent "i+, as it is the #ai#u# a#ount o "i+, so the a++arent "i+ )an a++ear to $eanythin& ro# 0IJ to the #ai#u# true "i+(

102



Figure 1: ip and strike of a (edding plane.

n this "ia&ra#, the "i+ is 30IJ, 'ith a stri*e north/south 0IJ/180IJ, the "i+ "ire)tionis 270IJ( n a &eolo&i)al #a+, sy#$ols are use" or the "i+ an" stri*e( The stri*e isre+resente" $y a $ar, an" the "i+ $y a #ar* on the stri*e $ar on the downdip "ire)tion'ith the "i+ 'ritten alon&si"e, as sho'n on the #a+ $elo' let(

&eolo&i)al )ross se)tion )an $e "ra'n ro# the #a+ sho'in& the su$sura)e stru)ture($%iously, only eatures 'hi)h )an $e seen on the sura)e )an $e re+resente"( The )ross-se)tion $elo' ri&ht is "ra'n usin& the %alues in the #a+ alon&si"e(

Figure 2a: A geological map Figure 2: A cross section of the map

te)hniHue 'hi)h is use" oten is to +lot %alues o "i+ an" "i+ "ire)tion on a stereo&ra#( stereo&ra# or stereonet or he#is+heri)al +roe)tion is a 'ay o re+resentin& 3-"i#ensional "ire)tions on a 2-"i#ensional sura)e( The net is a +roe)tion ro# the +oint

onto the eHuator( net is sho'n $elo'(

103



The #e)hanis#s o +lottin& +oints is sho'n in the net 4 "ia&ra#s(

1 2

The +oints are +la)e" all aroun" thes+here re+resentin& 3D s+a)e(

The +oints are +roe)te" "o'n onto theeHuatorial +lane on a line 'hi)h #eets u+ at the

south +ole

3 4

The +oints are then .#o%e". onto the +lane, 'hi)h is your stereonet

The inal stereonet(

To +lot a $e" onto the stereonet, use the ollo'in& &ui"e(

1( ?ut tra)in& +a+er on stereonet

2( Dra' aroun" the )ir)u#eren)e *no'n as the +ri#iti%e )ir)le or eHuator, an"#ar* on orth an" #ay$e outh

3( To +lot a +oint 'ith a 30IJ "i+ in a "ire)tion o 130IJ, 'ritten 30/130 +lot a +oint on the eHuator 130IJ aroun"

4( Then rotate the tra)in& +a+er so that the +oint youF%e ust +lotte" lies at 90IJ

104



5( Then )ountin& 30IJ in ro# the e"&e #ar* a se)on" +oint( This is the +oint30/130

si#ilar #etho" is use" to +lot a +ole to $e""in&, that is, a line 'hi)h is +er+en"i)ular tothe $e""in& sura)e(

1( ?ut tra)in& +a+er on stereonet

2( Dra' aroun" the )ir)u#eren)e *no'n as the +ri#iti%e )ir)le or eHuator, an"#ar* on orth an" #ay$e outh

3( To +lot a +ole to a $e" 'hi)h is "i++in& at 30IJ, in a "ire)tion o 130IJ, 'ritten30/130 +lot a +oint on the eHuator 130IJ aroun"

4( Then rotate the tra)in& +a+er so that the +oint youF%e ust +lotte" lies at 90IJ

5( Then )ountin& 30IJ o"t from the centre to the o++osite si"e to your irst +oint,

#ar* a se)on" +oint( This is the line +er+en"i)ular to the +lane "i++in& 30/130

n a stereonet a line is re+resente" $y a +oint an" a +lane $y a line(

F*%

ol"in& o ro)*s is )ause" $y the )o#+ression o ro)*s( This o))urs slo'ly, o%er a lon& +erio" o ti#e( this ha++ene" Hui)*ly, the ro)*s 'oul" $rea*, an" fa"lt ( This is "ue tothe #e)hani)al +ro+erties o ro)*s, na#ely itFs +lasti) nature( a ro)* is stret)he" slo'ly,then it 'ill $eha%e in a "u)tile ashion( stret)he" Hui)*ly, the ro)* $eha%es in a $rittle

ashion( This $eha%ior )an $e #i#i)*e" $y usin& lu-Ta)( ty+i)al ol" is sho'n $elo',outlinin& the ter#s use" in "es)ri$in& ol"s(

Figure 3: )omenclat"re "sed when descri(ing folds

;in&e:here )ur%ature o the ol" is at a #ai#u#

rest > Trou&h:here ol" sura)e rea)hes a #ini#u# an" #ai#u# res+e)ti%ely

105



Li#$:e"s $et'een t'o hin&es

ntior# > ynor#:on%e u+'ar"s or )on%e "o'n'ar" ol"s res+e)ti%ely

nti)line > yn)line:l"er or youn&er $e"s at the )ore res+e)ti%ely( an $e use" in )onun)tion 'ithantior# an" synor#, i(e( an antior#al syn)line

ol"s are )lassiie" $y sha+e an" the )hronolo&i)al or"er o ro)*s in the#( The sha+e o aol" is "es)ri$e" $y the an&le $et'een the li#$s, 'hi)h are &i%en the ter#s: gentle 1215678, open 12678, close 3678, tight 93678 or isoclinal9678(The )hronolo&i)al or"er o the ro)*s in a ol" are "es)ri$e" $y syn)line an" anti)line, as"es)ri$e" a$o%e(

ee i you )an i"entiy so#e eatures on the +i)ture $elo'(((

Figure 4: %"lworth co&e, orset

106



F&#

aults are )ause" $y short-ter# stress on ro)*s( They o))ur "is)ontinuously alon& fa"lt planes, an" are the )ause o #ost earthHua*es( aults are )lassiie" in ter#s o the ty+e o or)e )ausin& the ault 'hi)h "eter#ines the "ire)tion o #o%e#ent( There are #anyter#s use" in "es)ri$in& aults( These are sho'n in the "ia&ra# $elo'(

Figure 5: Fa"lt nomenclat"re.

The stri*e is the horiontal "istan)e #o%e"( The thro' is the %erti)al "istan)e an" thehea%e is the "istan)e #o%e" +er+en"i)ular to the ault(

The ty+es o ault, 'ith arro's sho'in& #otion, are sho'n $elo':

D!&1&' N&' M*% *3 F*'&!*$...

or#al ault !tension tension

Ce%erse ault or Thrust o#+ression

107



tri*e li+ hear

aults rarely all ea)tly into these )ate&ories, as they ha%e so#e o the other ty+es o #otion as 'ell, +arti)ularly so#e tri*e li+ an" rotational #otion( aults )an also $ereacti&ated , #eanin& a nor#al ault )an $e .reuse". at a later ti#e in a )o#+ressionalre&i#e( This +ro"u)es )o#+le drag folds alon& the si"e o a ault( Dra& ol"s o))ur asthe ro)* is $ent "ue to the #o%e#ent o the ault(

C*$+#!*$

tru)tural &eolo&y is the stu"y o the #e)hani)s o ro)* an" ro)* or#ations( tru)turesin)lu"e ol"s, ault an" "i++i&n& strata( There are a lot o te)hniHues use" to stu"ystru)ural &eolo&y in)lu"i& #easurin& "i+ an" stri*e or "i+ "ire)tion an" stereonet +roe)tions( There are lots o ter#s use" to "es)ri$e $oth ol"s an" aults, 'hi)h not only"es)ri$e the stru)ture $ut i#+ly so#e #o"e o or#aiton(

R3$+

( ?lu##er, D( M)=eary, 1997( Ph2!+& G**12( uy t( Alein, ( ;url$ut, 1997( M&$#& *3 M!$&*12( uy t

108









I$*%#+!*$ * S%!'$**12

e", 01/24/2007 - 13:21

A*# h &#h*


I$*%#+!*$

e"i#entary ro)*s are #a"e $y the a))u#ulation o +arti)les o ol"er ro)*s, either as)lasts )hun*s o ro)*s or as #ineral &rains, )he#i)ally or $io&eni)ally +re)i+itate"(lasti) se"i#entary ro)*s are +rin)i+ally )lassiie" on the $asis o &rain sie an" thenurther "i%i"e" in ter#s o #ineralo&y( ne o the #ost i#+ortant thin&s se"i#entaryro)*s )an tell us a$out is +alaeoen%iron#ents - an)ient en%iron#ents( This is "one $yloo*in& at the se"i#entary stru)tures an" the ossils )ontaine" 'ithin the ro)*s( They arealso an i#+ortant resour)e or oil, &as an" )oal(

This arti)le )on)entrates on )lasti) se"i#entary ro)*s( The )ar$onate tutorial or #oreinor#ation on a )he#i)ally +re)i+itate" se"i#entary ro)*s(

C&!3!+&!*$

lassii)ation o se"i#entary ro)*s is $ase" +rin)i+ally on &rain sie( =rain sie is#easure" in #illi#etres an" is the a++roi#ate "ia#eter o a sin&le &rain( There arese%eral ai"s or esti#atin& &rain sie in the iel" as 'ell as #ore so+histi)ate" ai"s 'henusin& thin se)itons o se"i#entary ro)*s un"er a #i)ros)o+e( The ta$le $elo' &i%es the&rain sies an" na#es o the )o##on se"i#entary ro)*s(

109

http://www.geologyrocks.co.uk/tutorials/introduction_to_carbonates

http://www.geologyrocks.co.uk/tutorials/introduction_to_carbonates



lassii)ation o )lasti) se"i#entaryro)*s $ase" on &rain sie(D!&' ('')

S%!'$ N&' R*+7 T2

K256 oul"er

Cu"a)eouson&lo#erate orre))ia

et'een 256 an" 64 o$$le

et'een 2 an" 64 ?e$$le

et'een 2 an" 0(625 an" rena)eous an"stone

et'een 0(625 an" 0(0039 ilt

r&illa)eous

siltstone

0(0039 laylaystone or#u"stone

: )on&lo#erate has roun"e" )lasts, a $re))ia has an&ular )lasts(

on&lo#erate( ?hoto $y Ti# %ani)(

Mu"stone(

110



an"stone(

Li#estone(

T"#

Tetures in se"i#entary ro)*s "e+en" on the ty+e o &rains #a*in& u+ the ro)*(

• Coun"ness - the "e&ree o roun"in& o a &rain( ot to $e )onuse" 'ith s+heri)ity(=rains )an $e ang"lar to well ro"nded. 'ell roun"e" &rain has &enerally tra%ele"urther $eore "e+osition(

Figure 1: *o"nding of clasts

• +heri)ity - "e&ree to 'hi)h &rain is a +ere)t s+here( Does T "e+en" onroun"ness(

• ortin& - the a#ount o "ierent sie" &rains in a ro)*( Can&es ro# %ery +oor to'ell sorte"(

•

Matri or )e#ent - the iner &rains in a ro)* #atrior a )he#i)al +re)i+itate)e#ent hol"in& the ro)* to&ether( o##on )e#ents are )al)ite or Huart(

111



Figure 2: emonstration of matri: and clasts

• o#+eten)e - the .tou&hness. o a ro)*(

ther +ro+erties o a se"i#entary ro)* are +orosity an" +er#ea$ility( The a$ility to store

lui" e(&( oil, &as or 'ater is the +orosity( The +orosity is e+resse" as a +er)enta&e an""e+en"s on the a#ount o +ore s+a)e in the ro)*( The a$ility to allo' a lui" to +assthrou&h a ro)* is the +er#ea$ility( lui" )an +ass throu&h usin& )ra)*s, issures or s+a)e $et'een &rains( hi&h +orosity ro)* )an ha%e a lo' +er#ea$ility i the +ore s+a)e "oesnot )onne)t in three "i#ensions

S#+#

The stru)tures in a ro)* tell us a &reat "eal a$out the +alaeoen%iron#ent( This is 'hereone o the &reat sayin&s in &eolo&y )o#es in use:

.The present is the key to the past . - the la' o unior#atarianis#

This essentially #eans i 'e )an un"erstan" 'hat +ro)esses o))ur to"ay, or ea#+le, theor#in& o ri++les in a ti"al #u", then these +rin)i+les )an $e a++lie" to the &eolo&i)alre)or"( elo' are so#e ea#+les o se"i#entary stru)tures an" 'hat or#e" the#(

way"p stru)ture tells us 'hi)h 'ay u+ the $e" 'as ori&inally "e+osite"( =ra"e" $e""in& usually o))urs 'ith the )oarse &rains at the $otto#( you in" so#e &ra"e" $e""in& 'ith )oarse &rains at the to+, then the $e" has +ro$a$ly $een te)toni)ally turne"u+si"e "o'n e(&( $y ol"in&(

112



ross e""in& or stratii)ation( The entire "une

as aroun" a #etre in hei&ht(These )ross $e"s 'ere or#e"in a shallo' lu%ialen%iron#ent, 'hi)h )an"eter#ine" usin& the relati%ely +oor sortin& o the san"stone(

Loa" )asts an" la#estru)tures, or#e" $y hea%ysan" sHuashin& the #ore#o$ile #u" u+'ar"s( ?hoto $yTi# %ani)(

This is a'ay u+ stru)ture as it thela#es that ha%e to #o%eu+'ar"s(

113



Mu")ra)*s or#e" ro# the"ryin& out o #u" an" then +reser%e" in the ro)*( Thes)ale on the let sho's)enti#etres an" in)hes(

C*$+#!*$

e"i#entary ro)*s are or#e" ro# ra&#ents o other, ol"er ro)*s, or are +re)i+itate"(They are $roa"ly )lassiie" $y &rain sie, althou&h #ore "etaile" )lassii)ation s)he#eseist( e"i#entary ro)*s are "es)ri$e" usin& ter#s su)h as roun"in&, sortin& an"s+heri)ity( e"i#entary ro)*s also )ontain stru)tures, su)h as )ross-$e""in& an""essi)ation )ra)*s 'hi)h )an &i%e )lues a$out the en%iron#ent in 'hi)h they or#e"(o#e stru)tures are also 'ay-u+ stru)tures 'hi)h )an hel+ "eter#ine i a ro)* is in-situor has $een ae)te" $y te)toni) #o%e#ent(

R3$+

( ?lu##er, D( M)=eary, 1997( Ph2!+& G**12( uy t

114






I$*%#+!*$ * I1$*# P**12

Mon, 01/22/2007 - 22:18

A*# h &#h*


I$*%#+!*$

&neous ro)*s are or#e" or# the )oolin& o #olten ro)*, #a&#a( They are )rystalline,'hi)h #eans they are #a"e u+ o )rystals oine" to&ether( There are #any "ierent ty+eso i&neous ro)*s $ut they all into t'o %ery $roa" )ate&ories< intrusi%e an" etrusi%e(ntrusi%e ro)*s are i&neous ro)*s 'hi)h or# at "e+th( They )ool slo'ly, ta*in& tens o thousan" o years to )ool( They ha%e lar&e )rystals, tens o #illi#etres in sie( !trusi%ero)*s are those 'hi)h ha%e eru+te" ro# %ol)anoes( They ha%e %ery s#all )rystals, not%isi$le to the na*e" eye, as they )oole" Hui)*ly( )ourse there is e%ery &rain sie +ossi$le in $et'een these t'o etre#es(

Ch'!2

The )he#istry o i&neous ro)*s is Huite )o#+li)ate"( t "e+en"s on t'o thin&s< e%olutionan" sili)a saturation( n this tutorial 'e 'ill )on)ern oursel%es 'ith the ee)t o e%olutiononly, the sili)a saturation 'ill $e assu#e" to $e )onstant( &neous ro)*s e%ol%e as they)ool( This +ro)ess is )alle" "ierentiation( The #e)hanis# or this +ro)ess is as ollo's:

1( LiHui" ri)h in #inerals , an" (

2( Ce#o%e #ineral as it )rystallises at a hi&her te#+erature than an" ( LiHui"is relati%ely enri)he" in #inerals an" (

3( Ce#o%e #ineral as it )rystallises at a hi&her te#+erature than ( LiHui" is no')o#+letely #ineral (

115



The #inerals are re#o%e" in or"er o o'enFs Cea)tion eries i&ure 1(

Figure 1: $owen;s reaction series

s you )an see, i you re#o%e oli%ine, the #a&#a 'ill $e)o#e #ore enri)he" in +yroenes et)( This +ro)ess )ontinues until only Huart is let( This lea"s us to theollo'in&, si#+le, i"entii)ation Ta$le 1(

"entii)ation o &neous Co)*sCo)* Ty+e

asi)une%ol%e"

nter#e"iate )i"i) e%ol%e"

Minerals

oli%ine, +yroene,

a#+hi$ole,)al)iu# +la&io)lase

)al)iu# an" so"iu# +la&io)lase, 'ith

so#e oli%ine, +yroenes an"a#+hi$oles

so"iu# +la&io)lase,

+otassiu# +la&io)lase an"Huart

#ount o sili)alo' hi&h

#ount o a2 an" A 2 lo' hi&h

#ount o a, e an" M&hi&h lo'

116



T"# : N&'

&neous ro)*s ha%e #any tetures 'hi)h tell us a$out their )oolin& histories an"/or )he#istry( n &eneral ro)*s 'hi)h ha%e )oole" ra+i"ly are ine &raine", that is 'ith &rains'hi)h are not %isi$le to the na*e" eye( Co)*s 'hi)h ha%e )oole" slo'ly ha%e lar&e

&rains, so#eti#es as lar&e as se%eral )enti#etres a)ross( This sie %ariation arises as&rains &ro' aroun" a nu)leus o so#e sort, i(e a #inute &rain( The slo'er the )oolin& the#ore ti#e &rains ha%e to &ro' an" a#al&a#ate( =rains 'hi)h sho' their true sha+e aresai" to $e e"hedral ( =rains 'hi)h sho' no sha+e are anhedral ( sin& this inor#ation,the or"er o &rain &ro'th )an $e 'or*e" out( or ea#+le, a ro)* #ay ha%e lar&eeuhe"ral Huart &rains, 'hi)h are surroun"e" $y anhe"ral el"s+ar( The Huart &re' irstas it ha" s+a)e, the el"s+ar then &re' aroun" the Huart(

ther eatures seen are:

• P*h2!!+ "# - lar&e &rains +heno)rysts surroun"e" $y #u)h iner &rains

&roun"a#ss( This i#+lies that the lar&e &rains &re' slo'ly at "e+th, the #a&#a'ith the &rains in it, then rose u+ in the )rust, )oolin& #u)h #ore Hui)*ly or#in& theine &rains the #atri(

• E"*#!*$ - o))urs 'ithin &rains on )ertain #inerals +yroenes an" el"s+ars( This)an &i%e an in"i)ation o +ressure an" hen)e "e+th(

• X$*!h - $its o the ro)* into 'hi)h the #a&#a intru"e"• C#'#& &2 - 'hen a #ineral &ro's 'hi)h is "enser than the #a&#a, it 'ill sin*

to the $ase o the )ha#$er )ausin& a )u#ulate layer( Minerals #ay or# ro# liHui"tra++e" $et'een the &rains - interstitial #inerals(

The na#e &i%en to an i&neous ro)* "e+en"s on itFs #ineralo&y $asi), inter#e"iate or a)i"i) an" the &rain sie( This is su#e#rise" in Ta$le 2(

a#es o&neousCo)*sR*+7 T2

B&!+ (#$4*4%) I$'%!& A+!%!+ (4*4%)

M!$& oli%ine, +yroene,a#+hi$ole, )al)iu# +la&io)lase

)al)iu# an" so"iu# +la&io)lase, 'ith so#eoli%ine, +yroenes an"a#+hi$oles

so"iu# +la&io)lase, +otassiu# +la&io)lasean" Huart

F!$

G&!$%

asalt n"esite Chyolite

117



N&'

C*&

G&!$%

N&'

=a$$ro Diorite =ranite

I1$*# R*+7 F*'&!*$

&neous ro)* $o"ies are either intrusi%e or etrusi%e( !trusi%e $o"ies are la%a lo's( these o))ur un"er 'ater they or# +illo' la%as( n lan" they )an or# la%a tu$es, aa+ronoun)e" ah-ah an" loo*s $lo)*y or +ahoehoe 'hi)h loo*s ro+ey(

Figure 2: Acti&e, ropy pahoehoe on the so"thso"thwest flank of Alae in <awaii

=olcanoes )ational ark. Co"rtesy of >'+' <awaiian =olcano #(ser&atory

ntrusi%e $o"ies or# 'hen #a&#a is ine)te" into eistin& ro)* layers( "y*e is a $o"y'hi)h )uts a)ross the )ountry host ro)* i&ure 2( sill is +arallel to the $e""in&layers( The $a*e" #ar&in is an area in the )ountry ro)*, in )onta)t 'ith the i&neous $o"y,'hi)h has $een ther#ally #eta#or+hose"( The )hille" #ar&in is the area in an i&neous $o"y, in )onta)t 'ith the )ountry ro)*, 'hi)h )oole" Hui)*er than the rest o the ro)* "ueto the te#+erature "ieren)e $et'een the #a&#a an" the )ountry ro)*( These eatures

118

http://hvo.wr.usgs.gov/

http://hvo.wr.usgs.gov/



are not al'ays %isi$le( The s)ale o these $o"ies is ro# #illi#etres to tens or e%enhun"re"s o #etres(

The lar&est o i&neous $o"ies is a +luton or $atholith( These are #assi%e, hun"re"s o *ilo#etres in sie( The #oors o orn'all an" De%on are out)ro+s o a #assi%e $atholith(

Figure 3: 0ntr"si&e igneo"s (odies. *edrawn from l"mmer / Mc+eary 1!!8

S*' P!+# O3 I1$*# R*+7

enolith "ar* +at)h in a $asalti) sill( ?hoto $y Ti# %ani)(

119



)lose u+ o so#e &ranite( The &rains are rou&hly 2)# in sie( The "ar* &rains are $iotite( The 'hite &rains are Huart an" the +in* &rains are ortho)lase el"s+ar( ?hoto $yTi# %ani)(

$asalti) ro)*( This ro)* is +art o a la%a lo' +ahoehoe( The re" )olour is "ue tooi"isin& o the iron #inerals( ?hoto $y Ti# %ani)(

+hoto o so#e +illo' la%as( These or#e" un"er'ater an" )oole" Huite Hui)*ly( Thesha+e is "ue to the sura)e )oolin& %ery Hui)*ly, or#in& a .s*in.( The net +illo' then $ro*e the .s*in. or#in& the net +illo'( ?hoto $y Ti# %ani)(

120



This ro)* sho's a +or+hyriti) teture( The lar&e &rains +heno)rysts are el"s+ar, 'hi)hare surroun"e" $y a #atri o Huart, el"s+ar an" #i)a( ?hoto $y Ti# %ani)(

C*$+#!*$

&neous ro)*s or# ro# the )oolin& o #olten ro)*: #a&#a( They are )lassiie" usin&)rystal sie an" )he#istry( The si#+lest )lassii)ation ty+e uses three )he#i)al"es)ri+tors< $asi), inter#e"iate an" a)i"i)< an" t'o &rain sies< ine an" )oarse( The

)he#istry o #a&#a alters as it )ools a))or"in& to o'enFs Cea)tion eries( &neousro)*s or# &eolo&i)al $o"ies su)h as "y*es an" sills as intrusi%e stru)tures an" %ol)anoesan" la%a lo's as etrusi%e eatures(

121



I$*%#+!*$ * C&*$&

Mon, 02/05/2007 - 15:52

A*# h &#h*


I$*%#+!*$

ar$onates are ro)*s )o#+ose" #ainly o )al)iu# )ar$onate, a3( o#e ea#+les o )o##on )ar$onate ro)*s are li#estones an" )hal*( ar$onates or# $y +re)i+itationro# 'ater< either strai&ht ro# the 'ater, or in"u)e" $y or&anis#s, to #a*e their shellsor s*eletons, an" they or# in #any en%iron#ents i&ure 1(

Figure 1: 'ome typical en&ironments that car(onates can form. *edrawn from T"ckerand ?right 1!!8.

122



M!$&*12

There are three #ain #inerals that or# )ar$onates:

• al)ite a3, 'hi)h )o#es in hi&h #a&nesiu# an" lo' #a&nesiu# or#s(• ra&onite a3, 'hi)h has a "ierent stru)ture to )al)ite(• Dolo#ite aM&32, a #a&nesiu# ri)h )ar$onate +ro"u)e" $y "ia&enesis(

nly lo' #a&nesiu# )al)ite is sta$le at sura)e +ressure an" te#+eratures( t is thereorethe #ost )o##on #ineral in an)ient )ar$onates( ;o'e%er, #ost #o"ern )ar$onates are)o#+ose" o ara&onite as this is the #ineral that #ost $iolo&i)al or&anis#s )reate to#a*e their shells or s*eletons( !a#+les o or&anis#s that +ro"u)e ara&onite shells are $i%al%es sea shells, &astro+o"s snails an" ;ali#e"a a &reen al&ae( r&anis#s that +ro"u)e a )al)ite shell in)lu"e $ra)hi+o"s a rare ty+e o sea shell an" ostro)o"s a s#all)rusta)ean(

C*'*$$

ar$onates )an $e #a"e o se%eral )o#+onents( These are:

• io)lasts(• oi"s(• ?eloi"s(• ntra)lasts(• Mi)rite(•

+arite(io)lastsio)lasts are ra&#ents o "ea" sea )reatures( These in)lu"e shells i&ure 2 an")orals( The )reatures +re)i+itate the )ar$onate in or"er to +ro"u)e so#e *in" o stru)ture(

123



Figure 2: A (ioclastic limestone. <ere the (ioclasts are (i&al&es of Car(onifero"sage.

oi"soi"s are roun"e" &rains or#e" $y +re)i+itation o )al)ite aroun" a nu)leus to +ro"u)e )on)entri) )ir)les i&ure 3( They or# in 'ar#, shallo' 'aters, 'ith a

stron& ti"al )urrents( a%e a)tion #ay also )ontri$ute to their near-s+heri)alsha+e(

Figure 3: The str"ct"re of an ooid. *edrawn from T"cker and ?right 1!!8(

?eloi"s?eloi"s are san" sie" &rains 100-150 #i)ro#eters o #i)ro-)rystalline)ar$onate( They are &enerally roun"e" or su$-roun"e"( They ori&inate ro# e)al +ellets, al&ae an" #u" )lasts( They are so#eti#es oun" )lu#+e" to&ether, in aor#ation *no'n as a grapestone(

ntra)lastsntra)lasts are )last o other li#estone that a++ear in youn&er li#estones( They)an $e Huite "ii)ult to "istin&uish at ti#es, as they #ay $e #a"e o a si#ilar ro)* as that 'hi)h en)ases it( or ea#+le, har"&roun"s )an ro# 'hen sea 'ater lo's throu&h )ar$onate se"i#ent, lithiyin& it ra+i"ly( u$seHuently, thehar"&roun" #ay $e $ro*en u+ an" in)or+orate" into the surroun"in& se"i#ent(

Mi)riteMi)rite is #i)ro)ystalline )ar$onate #u", 'ith &rains less than 4 #i)ro#eters(

+arite+arite is )oarser than #i)rite, 'ith a &rain sie o #ore than 4 #i)ro#eters an" is)rystalline(

oth #i)rite an" s+arite or# the matri: or cement in )ar$onate ro)*s(

124



C&!3!+&!*$

There are t'o #ain #etho"s o )lassiyin& )ar$onate ro)*s< Dunha#Fs an" ol*Fs)lassii)ation( elo' is Dunha#Fs )lassii)ation 'hi)h uses the teture o the ro)* to)lassiy the )ar$onate( Dunha#Fs )lassii)ation is useul or iel" 'or*(

Ce)o&nia$le De+ositional Teture rystalline

o#+onents not $oun" to&ether ri&inal)o#+onents $oun"to&ether

C2&!$

C&*$&

ontains Mu" La)*s #u"an" is &rainsu++orte"

B*#$%*$

Mu" u++orte" =rainu++orte"

G&!$S*$

10

&rains

K10 &rains

P&+7*$M#%*$ W&+7*$

125



ol*Fs )lassii)ation is %ery useul or )ar$onates in thin se)tion( t )lassiies )ar$onates $ase" on their )o#+onents see a$o%e an" the #atri/)e#ent $in"in& the )o#+onentsto&ether(

lasts

I$+& '&!&

Mi)rite +arite

ossils io#i)rite ios+arite

oi"s o#i)rite os+arite

?eloi"s ?el#i)rite ?els+arite

ntra)lasts ntra#i)rite ntras+arite

C*$+#!*$

ar$onate ro)* are se"i#entary ro)*s ro# ro# )al)iu# )ar$onate, a03( al)iu#)ar$onate is either the #ineral ara&onite, hi&h #a&nesiu# )ar$onate or lo' #a&nesiu#)ar$onate( nly lo' #a&nesiu# )ar$onate is sta$le at sura)e +ressures an"te#+eratures, $ut #ost #o"ern )ar$onate is ara&onite( ar$onates are or#e" ro#%arious )o#+onents, 'hi)h in)lu"e ooi"s, +eloi"s, )lasts an" $iolo&i)al re#nants(ar$onates are )lassiie" $y either ol*Fs or Dunha#Fs )lassii)ation s)he#es(

R3$+

M( !( Tu)*er an" ?( ri&ht, 1990( C&*$& S%!'$**12( uy t(

126





P& T+*$!+5 A$ I$*%#+!*$

un, 01/21/2007 - 21:48

A*# h &#h*


I$*%#+!*$

?late te)toni)s is the theory that un"er+ins #ost o #o"ern &eolo&y( The $asi) i"ea is thatthe sura)e o the !arth is #a"e u+ o se%eral se&#ents - +lates( These +lates #o%earoun" the &lo$e 'hile $ein& )reate" an" "estroye" at their #ar&is( This theory hel+s toe+lain #any thin&s, su)h as the ro)* ty+es that in"i)ate "esert )li#ates in north !n&lan"(Cather than ha%e to #o%e the )li#ati) $elts, it is the )ontinent itsel that has #o%e"(ther thin&s that +late te)toni)s e+lains is the sha+e o the )ontinents, the a)t that the)oastlines o ri)a an" outh #eri)a it to&ether( This is o$%ious loo*in& at any #a+i&ure one( The $oun"aries o the +lates, re&ar"less o ty+e are #ar*e" $y earthHua*esthe $la)* "ots an" so#e $y %ol)anoes(

Figure 1: A map of the plates on the arth. Modified from l"mmer and Mc+eary1!!8.

127



Th L!h*h

The +late in +late te)toni)s is the *no'n as the lithos+here( The 'or" lithos+here #eans.ro)* layer.( The lithos+here is #a"e u+ o the )rust an" the u++er#ost #antle i&ure2( t a%era&es a$out 100*# in thi)*ness( The layer $elo' the lithos+here is the

asthenos+here - 'hi)h #eans .'ea* layer.( The lithos+here ee)ti%ely .sli"es. o%er this'ea* layer( There are t'o ty+es o lithos+here: )ontinental an" o)eani)( !a)h has itFs o'nset o uniHue eatures an" stru)ture( oth ty+es o lithos+here )an eist 'ithin a sin&le +late, or ea#+le the orth #eri)an +late has $oth )ontinental an" o)eani) lithos+here(;o'e%er, the )ontinental lithos+here )an $e #u)h thi)*er than 100*#, es+e)ially in ol",sta$le, ?re)a#$rian areas( n"er these areas, roots or *eels or#, sti)*in& the )ontinental)rust into the #antle( The lithos+here is &enerally ri&i" that is, it )ra)*s an" "oes not $en"(

Figure 2: %ithospheric str"ct"re. %eft shows the oceanic lithosphere@ the right shows thecontinental lithosphere. *edrawn from eary and =ine 1!!B8.

128



C*$#+!4 P& M&1!$

onstru)ti%e +late #ar&ins, also *no'n as "i%er&ent +late #ar&ins or #i"-o)ean ri"&esare 'here +lates are )reate"( t a #i"-o)ean ri"&e, #a&#a 'ells u+ )reatin& ne' o)eani)lithos+here( The ri"&es )ir)le the +lanet, o))urrin& in all the #aor o)eans(

#i"-o)ean ri"&e )onsists o se)tions o ri"&e se+arate" $y transor# aults i&ure 3(The ri"&e is ele%ate" 'ith res+e)t to the o)ean loor "ue to the hi&h heat lo' $eneath(The heat lo' ele%ates the ri"&e "ue to the asso)iate" re"u)tion in "ensity( They arety+i)ally 2*# hi&her than the ty+i)al o)ean "e+th o 4*#( t the transor# aults, the"e+th "oes in)rease sli&htly(

s 'ith all +late #ar&ins, )onstru)ti%e +late #ar&ins are asso)iate" 'ith seis#i)ity(;o'e%er, the earthHua*es on a #i"-o)ean ri"&e are ar ro# any hu#an lie an" usuallylo' in #a&nitu"e, an" thereore not "an&erous( They are also shallo' an" )on)entrate"aroun" the transor# aults(

The #a&#a that 'ells u+ at ri"&es "oes not %ary in )o#+osition ro# ri"&e to ri"&e( t isal'ays $asi) tholeitii) in )o#+osition( t or#s stru)tures )alle" +illo' la%as see thethis +i)ture, or ea#+le( The "y*es an" )u#ulates in the lithos+here are also $asi) in)o#+osition(

Figure 3: A mid ocean ridge, which is a constr"cti&e plate (o"ndary.

129

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http://www.geologyrocks.co.uk/picdetail.php?picture=4



D#+!4 P& M&1!$

"estru)ti%e +late #ar&in or su$"u)tion one is 'here +lates are "estroye"( They are thesour)e o #aor earthHua*es an" %ol)anis#, es+e)ially aroun" the ?a)ii) 'here theyor# .The Cin& o ire.( There are three ty+es o "estru)ti%e #ar&ins - those 'here

o)eani) lithos+here #eets o)eani) lithos+here, )ontinent-)ontinent )ollisions an" that'here )ontinental lithos+here #eets o)eani) lithos+here( The eatures in ea)h )ase aresi#ilar( ;o'e%er, a )ontinent-)ontinent )ollision results in little or no %ol)anis#( Therethree ty+es o "estru)ti%e +late #ar&ins i&ure 4, "es)ri$e" $elo'(

The seHuen)e o the i&ures $elo' is not )oin)i"ental( The only lithos+here that )anusually su$"u)t is o)eani) lithos+here, "ue to its hi&h "ensity )o#+are" to )ontinentallithos+here( ty+i)al seHuen)e o e%ents or a su$"u)tion are:

• u$"u)tion starts, either o)ean-o)ean or o)ean-)ontinent(• su$"u)tion starte" 'ith o)ean-o)ean, then it #ay +ro&ress to o)ean-)ontinent i one

o the o)eani) +lates has so#e )ontinental lithos+here in it(• $oth +lates ha%e )ontinental lithos+here 'ithin, then )ontinent-)ontinent )ollision

'ill o))ur(

ontinent-)ontinent )ollision results in #ountain $uil"in& or oro&enesis(

)ean-o)ean )ollision( ote the tren)han" %ol)ani) ar)( Ba+an is an ea#+le osu)h an islan" ar)(

)ean-)ontinent )ollision( The tren)h is

still there, $ut the %ol)anis# o))urs on the)ontinental )rust( The n"es #ountainsare an ea#+le o this situation(

130



The t'o +lates o%erri"e ea)h other,thi)*enin& the lithos+here an" +ro"u)in&#ountains( The ;i#alayas are a &oo"

ea#+le o this( ll #ountain )hains areor#e" in this 'ay( ote the la)* o%ol)anoes(

Figure 4: The three types of destr"cti&e margin. Modified from >'+' .

The *ey eatures o a su$"u)tion one are a tren)h an" %ol)ani) ar)( The tren)hes or#the "ee+est +arts o the o)ean( They are usually ille" in 'ith se"i#ent "eri%e" ro# the)ontinent an" .s)ra+e". o the su$"u)tin& o)eani) +late( This se"i#ent +a)*a&e is )alle"the accretionary prism( The %ol)anoes in "estru)ti%e +late #ar&ins are an"esiti) in o)ean-o)ean )ollisions an" an"esiti) to &raniti) in o)ean-)ontinent )ollisions( !arthHua*es in a"estru)ti%e #ar&in are #u)h lar&er an" )an o))ur at all "e+ths( They tra)e the +ath o thesu$"u)tin& sla$ as it +lun&es into the #antle( This )ur%e that the earthHua*es tra)e out is)alle" the enio None(

C*$4&!4 P& M&1!$

The )onser%ati%e +late #ar&in is easiest to un"erstan"( t is a stri*e-sli+ ty+e ault 'heret'o a"a)ent +lates #o%e alon&si"e ea)h other( The an n"reas ault is the #ost 'ell*no'n ea#+le an" is the $oun"ary $et'een the orth #eri)an +late an" the ?a)ii) +late( Lo)ate" in aliornia, , it +asses "ire)tly throu&h an ran)is)o( t has )ause"#any earthHua*es sin)e hu#ans inha$ite" the re&ion 'ith the $i&&est in histori)alre)or"s o))urin& on the 18th +ril, 1908( %er 700 +eo+le "ie"(

The ault itsel is aroun" 30 #illion years ol" an" has #o%e" a total "istan)e o so#e300*# in this ti#e aroun" an a%era&e o 10## a year(

131

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C*$+#!*$

?late te)toni)s i the ra#e'or* or all #o"ern &eolo&y( The theory states that the earthFssura)e is #a"e u+ o se%eral +lates that #o%e aroun", $ein& )reate" an" "estroye" at the +late #ar&ins( This results in earthHua*es an", on so#e ty+es o #ar&ins, %ol)anoes( The

three ty+es o #ar&in are )onser%ati%e, )onstru)ti%e or "estru)ti%e( onstru)ti%e #ar&insare the site o #i"-o)ean ri"&es( Destru)ti%e #ar&ins or# su$"u)tion one 'here a +lateis +ushe" un"erneath another(

R3$+

?( Aeary > (B @ine, 1996( G*& T+*$!+( uy t

( ?lu##er, D( M)=eary, 1997( Ph2!+& G**12( uy t

132








I$*%#+!*$ * M&'*h!+ P**12

e", 01/24/2007 - 13:12

A*# h &#h*


I$*%#+!*$

Meta#or+hi) +etrolo&y is the stu"y o ro)*s 'hi)h ha%e $een )han&e" #eta#or+hose" $y heat an" +ressure( They are $roa"ly )ate&orie" into re&ional an" )onta)t(Meta#or+his# is an etension o the +ro)ess 'hi)h or#s se"i#entary ro)*s ro#se"i#ent: lithii)ation( ;o'e%er, all ty+es o ro)*s< i&neous, se"i#entary an"#eta#or+hi), )an all $e #eta#or+hose"( Durin& #eta#or+his# no #eltin& ta*es +la)e(ll the )he#i)al rea)tions 'hi)h ta*e +la)e o))ur in the soli"-state(

F&+* C*$*!$1 Ch&&+!!+

The )hara)teristi)s o a #eta#or+hi) ro)* "e+en" on the ollo'in& a)tors:

1( o#+osition o +arent ro)*

2( Te#+erature an" ?ressure o #eta#or+his#

3( lui"

4( Ti#e

The )o#+osition o the +arent ro)* "oes not usually )han&e "urin& #eta#or+his# i it"oes it is then )alle" #etaso#atis#( The )han&es are the "ue to the #inerals )han&in&(

$asalt 'hi)h has aroun" 50 o sili)a 'ill +ro"u)e a #eta$asalt 'ith 50 sili)a(

Te#+erature an" +ressure ae)t the ro)* in ter#s o the #ineral asse#$la&e 'hi)h issta$le at the +ressure an" te#+erature o$taine"( The #inerals sta$le at the +ressure an"te#+eratures that #eta#or+hi) ro)*s rea)h are si#ulate" in a la$( This allo's &eolo&iststo loo* at a #ineral asse#$la&e an" &i%e a &oo" esti#ate o the +ressure an"te#+erature that the sa#+le 'as e+ose" to( This &i%es te)toni) inor#ation 'hi)h isuseul in other $ran)hes o &eolo&y(

133



lui" )han&es the )he#i)al )o#+osition o the ro)* $ein& #eta#or+hose" an" hen)e is)alle" #etaso#atis#( The a""ition o lui" )an ra"i)ally )han&e the ro)*(

Ti#e has an i#+ortant role as a ro)* 'hi)h is heate" to an etre#e te#+erature or ashort years +erio" o ti#e 'ill not $e altere" too #u)h( ro)* heate" or a lon&er

+erio" o ti#e #illions o years 'ill sho' )han&es(

C&!3!+&!*$

The )lassii)ation o #eta#or+hi) ro)*s is s+lit into )onta)t an" re&ionally#eta#or+hose" ro)*s( ter this it is "i%i"e" a))or"in& to the .a#ount. o #eta#or+his# that has ta*en +la)e an"/or on the #ineral )ontent(

C*$&+ M&'*h!' (&% *$ '!$& +*$$)

P&$ R*+7 M&'*h!+ *+7 D*'!$&$

M!$&Ch&&+!!+

Li#estone Mar$le al)itenterlo)*in& &rains( ies in'ea* a)i"

Guart an"stone Guartite Guart u&ary teture

hale;ornels +otte"Co)*

Mi)as Dar* )olour

R1!*$& M&'*h!' ($&' &% *$ %1 *3 '&'*h!')

T"# R*+7 N&' Ch&&+!!+

latey late +lits easily into sheets

et'een slate an" ?hylitte il*y lustre, s+lits into 'a%y sheets

134



s)histose

)histose )hist ?early loo*in&( il*y to tou)h

=neissi) =neiss a%y, 'hite an" "ar* layers

late( ?hoto $y Ti# %ani) )hist( ?hoto $y Ti# %ani)

=neiss( ?hoto $y Ti# %ani)Mar$le( ?hoto )ourtesy o Dr( Ci)har" us)h, esthester ni%ersity

C&# *3 M&'*h!'

C*$&+

ause" $y heatin& ro# an eternal sour)e( onta)t #eta#or+his# o))urs net to ani&neous $o"y( The "e&ree o #eta#or+his# "e)reases a'ay ro# the $o"y( This o))urs atairly shallo' "e+ths 10*#, as te#+erature not +ressure is the "o#inatin& a)tor(

135



R1!*$&

Ce&ional #eta#or+his# is )ause" $y hi&h +ressure an" te#+eratures usually "urin&#ountain $uil"in& ore&enesis( The etre#es o re&ionally #eta#or+hi) ro)*s are a hi&h +ressure, lo' te#+erature ro)* )alle" a $lues)hist an" a hi&h +ressure an" %ery hi&h

te#+erature ro)* )alle" a &ranulite( the ro)* is heate" to the +oint o #eltin&, $ut"oesnFt a)tually #elt, it is )alle" a #i&#atite(

C*$+#!*$

Meta#or+his# is the transor#ation o +re-eistin& ro)*s $y heat an" +ressure( Ti#e isalso an i#+ortant a)tor( Meta#or+his# is a )ontinuation o the +or)ess that turnsse"i#ent into ro)* lithii)ation( There are t'o #ain )auses o #eta#or+his#< )onta)t,'hih is )ause" $y )lose +roi#ity o a hot, i&neous $o"y< an" re&ional, 'hi)h is lar&er s)ale an" is )ause" $y te)toni) or)es( There are our #ain a)tors in "e)i"in& the ty+e o ro)* +ro"u)e" $y #eta#or+his#: )o#+osition o +arent ro)*, te#+erature an" +ressure

o #eta#or+his#, the role o lui"s an" ti#e( lassii)ation is $ase" on the ty+e o #eta#or+his#, the a#ount o )han&e an" the )o#+osition o the +arent ro)*(

R3$+

( ?lu##er > D( M)=eary, 1997( Ph2!+& G**12( uy t

136





G**1!+& T!'

Thu, 02/08/2007 - 13:39

A*# h &#h*


I$*%#+!*$

;o' "o 'e *no' the a&e o the !arthE ;o' "o 'e *no' the a&e o ro)*s 'e in"E Thereare t'o #ain 'ays to "ate ro)*s - a$solute "atin& an" relati%e "atin&( ter the ro)*sha%e a "ate assi&ne" to it, they )an $e +ut in so#e sort o or"er, an" the relati%e "ates'or*e" out( This is the &eolo&i)al ti#es)ale(

Th A1!$1 E&h

The !arth has a&e" a &reat "eal sin)e the in)e+tion o #o"ern &eolo&y( eore the 19th

entury, i$li)al inter+retations o the a&e o the !arth 'ere the a))e+te" %ie'( The #ost)o##on i&ure 'as 6000 years ol", $ase" on )ountin& the a&es o +eo+le #entione" in

the i$le, +arti)ularly the l" Testa#ent( ne s)holar, Bohn Li&htoot, state" the #o#ento )reation 'as 9:00 M, e+te#$er 17th , 3928 (

n 1862 Lor" Ael%in )al)ulate" an a&e o 20 to 40 #illion years, $ase" on )oolin& o the!arth ro# a #olten state( ther #etho"s o tryin& to "ate the !arth in)lu"e )al)ulatin&e%a+oration rates ro# the o)eans, usin& se"i#entation rates, erosion rates an" ti"alor)es $et'een the !arth an" the Moon( These #etho"s &a%e a&es o $et'een a e'#illion years an" 1 $illion years(

t 'asnFt until ra"ioa)ti%e "e)ay 'as "is)o%ere" that the true a&e o 4(6illion years4,600,000,000 yearsO 'as oun"(

A*# D&!$1

$solute "atin& is &ettin& an a)tual "ate, i(e( this ro)* is 5(67 #illion years ol"( The #ain#etho" or this is ra"ioa)ti%e "atin&( o, hereFs a $it o +arti)le +hysi)s(((

!le#ents ha%e isoto+es, that is the sa#e ele#ent 'ith a "ierent nu#$er o neutrons inthe nu)leus, $ut 'ith the sa#e nu#$er o ele)trons an" +rotons( o#eti#es these

137



isoto+es are unsta$le an" "e)ay to a #ore sta$le )oni&uration( Durin& "e)ay the nu)leuss+ontaneously "isinte&rates, +ro"u)in& ener&y an" +arti)les( There are t'o #ain #etho"so "e)ay an" $oth o the# in%ol%e the loss o +arti)les ro# the nu)leus(

• l+ha De)ay - loss o a heliu# nu)leus t'o +rotons an" t'o neutrons ro# the

nu)leus o the +arent• eta De)ay - a neutron turns into a +roton an" an ele)tron an" the ele)tron is e#itte"(

There are t'o other ty+es o "e)ay, &a##a an" ele)tron )a+ture or $eta-#inus, $ut&a##a o))urs alon& 'ith the others an" ele)tron )a+ture only o))urs in #an-#a"eisoto+es(

!a)h isoto+e has a uniHue hal-lie, 'hi)h is a )onstant an" relate" to the "e)ay )onstant(The hal-lie is the ti#e ta*en or hal the ra"ioa)ti%e isoto+e to $e re"u)e" $y hal( Thislea"s to e:ponential decay ro# 'hi)h the a&e o the isoto+e )an $e )al)ulate"( or so#e +roo )li)* here an" i you "onFt li*e #aths, ust loo* at the &ra+h(

The &ra+h i&ure 1 sho's the nu#$er o ra"ioa)ti%e nu)lei in an #ass o isoto+e,a&ainst ti#e t(

Figure 1: +raph depicting the n"m(er of ne"trons against time for a radioacti&e s"(stance.

The #ain +ro$le# 'ith this #etho" is *no'in& 0 - the ori&inal a#ount o the #aterial(This is "one usin& other #etho"s, 'hi)h are too a"%an)e" or this +a&e( 0 is *no'n

then a ro)* #ay $e "ate" i it )ontains ra"ioa)ti%e isoto+es 'hi)h ha%e or#e" 'ith thero)*( This only a++lies to i&neous an" in so#e )ontets, #eta#or+hi)( you try an" "atea se"i#entary ro)*, youFll &et a host o )onli)tin& a&es, as ea)h +arti)le #ay ha%e )o#ero# a "ierent sour)e ro)* an" hen)e $e "ierent in a&e(

138

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http://www.geologyrocks.co.uk/tutorials/exp_maths



R&!4 D&!$1

Celati%e "atin& is si#+ly sayin& that this $it is ol"er than that $it( This is #ost useul in ase)tion o ro)*, 'here it is )lear 'hi)h ro)* is at the $otto# an" hen)e is ol"er an"'hi)h is the u++er#ost an" is the youn&est( This #etho" )annot $e use" 'orl"'i"e,

$e)ause e%ery )ountry "oes not ha%e the sa#e ro)*s at the sa#e ti#e( To &et o%er this 'e)an use thin&s 'hi)h only eist o%er a short &eolo&i)ally s+ea*in& +erio" o ti#e an"ha%e a 'orl"'i"e "istri$ution - ossils, or #ore +re)isely a one fossil ( one ossilnee"s to $e:

• o##on• Ca+i"ly e%ol%in&• i"es+rea"• !asily i"entiia$le

=ra+tolites #a*e &oo" one ossils( you in" a ossil in one +la)e 'hi)h eiste" :#illion years a&o in )otlan" an" the sa#e ossil eists in #eri)a, the ro)*s are thesa#e a&e( This is ho' #ost o the early "atin& 'as "one(

ne o the #ain la's in &eolo&y is the la' o s"perposition( This si#+ly #eans that stu on to+ is youn&er than the stu $elo', if they are the ri&ht 'ay roun"( nother la' is thecrossc"tting la'( a ro)* is )ut $y another ro)*, then it is ol"er than the ro)* 'hi)h has)ut it( The "ia&ra# $elo' uses these +rin)i+als to &et the &eolo&i)al history(

Figure 2: Cross section of some geology, the history is detailed (elow. *edrawn from l"mmer / Mc+eary 1!!8

139



$rie history &oes so#ethin& li*e this:

• - "e+osite"• - intru"e"• > - tilte" an" ero"e"• - "e+osite" as D )uts , an" • D - intru"e"• D > ero"e", a&ain "ue to lat sura)e• ! - "e+osite"• ! - +ro$a$ly ero"e"

This #eans that not all the ro)* re)or" is there, so#e o , D an" ! #ay $e #issin&(There #ay $e other $e"s 'hi)h ha%e $een )o#+letely ero"e" o( you )anFt Huite see'hy this is, try the ste+-$y-ste+ &ra+hi)al a++roa)h, $y )li)*in& this lin*(

The 'hole seHuen)e )an $e a$solutely "ate" usin& the t'o intrusions, an" D( These, inturn, )an &i%e relati%e "ates to the others $y usin& the )ross-)uttin& relationshi+s seen inthe "ia&ra#(

Th G**1!+& T!'+&

The &eolo&i)al ti#es)ale )o%ers the 'hole o the !arthFs history( t starts at a$out 4(6illion 4,600,000,000 years a&o or 4600Ma Ma - Million years $eore +resent 'iththe or#ation o the solar syste# an" )ontinues ri&ht u+ to the +resent "ay( t is s+lit into4 !ras:

• ?re)a#$rian - 4600Ma to 550Ma• ?aleooi) - 550Ma to 250Ma• Mesooi) - 250Ma to 65Ma• enooi) - 65Ma to ?resent "ay

The eras are s+lit into +erio"s, 'hi)h are s+lit into e+o)hs( These are sho'n in the ta$le $elo'( The na#es use" are the ritish na#es an" so#e "ierent na#es #ay $e use" inother )ountries, es+e)ially orth #eri)a( The "ates sho'n are the a&es in 'hi)h thee+o)h starte"( The $ol" "ates are the start o +erio"s

140

http://www.geologyrocks.co.uk/tutorials/geotime_cross_cutting

http://www.geologyrocks.co.uk/tutorials/geotime_cross_cutting



E& P!*% E*+h A1

enooi)

Guaternary

;olo)ene 10,000 Pa

?leisto)ene 1(6Ma

eo&eneQ

?lio)ene 5(14Ma

Mio)ene 23(5Ma

?alaeo&eneQ

li&o)ene 35(5Ma

!o)ene 56Ma

?alaeo)ene 65Ma

Mesooi)

reta)eous

Late reta)eous 97Ma

!arly reta)eous 146Ma

Burassi) Late Burassi) 155Ma

Mi""le Burassi) 175Ma

!arly Burassi) 205Ma

141



Triassi)

Late Triassi) 230Ma

Mi""le Triassi) 242Ma

!arly Triassi) 251Ma

?aleooi)

?er#ian

Ne)hstein 260Ma

Cotlie&en"es 290Ma

ar$onierous

te+hanian 302Ma

est+halian 313Ma

a#urian 323Ma

@isRSan 341Ma

Tournaisian 353Ma

De%onian Late De%onian 371Ma

Mi""le De%onian 380Ma

!arly De%onian 409Ma

142



ilurian

?rR"olR 411Ma

Lu"lo' 423Ma

enlo)* 430Ma

Llan"o%ery 439Ma

r"o%i)ian

sh&ill 443Ma

ara"o) 464Ma

Llan"eilo-Llan%irn 476Ma

reni& 493Ma

Tre#a"o) 510Ma

a#$rian

Merioneth 515Ma

t Da%i"s 528Ma

aerai 550Ma

?re)a#$rian ontains r)hean an" ?roterooi) !ons 4600Ma

143



Q - the eo&ene an" ?alaeo&ene are )olle)ti%ely *no'n as the Tertiary(

The ta$le a$o%e has "ates $et'een +erio"s in lar&e, $ol" ont( DonFt 'orry to #u)h a$out#e#oriin& the others, not #any &eolo&ists )an list the# o the to+ o their hea"( you)an say 'hi)h +erio" 'as 300Ma, then thatFs &oo" enou&hO

C*$+#!*$

The earth is 4(6 illion years ol"( The ro)*s on the earth )an $e "ate" usin& relati%e"atin&, 'hi)h in%ol%es "atin& a ro)* 'ith res+et to another ro)*< or a$solute "atin&,'hi)h is &i%in& a nu#eri)al "ate to a ro)*( Celati%e "atin& is "one usin& ossils, the la'o su+er+osition or )ross-)uttin& relationshi+s( $solute "atin& is "one usin& ra"io#etri)#etho"s 'hi)h uses ra"ioa)ti%e ele#ents, su)h as raniu# or ?otassiu# to "ate a ro)*(

ll ro)*s )an $e arran&e" in the &eolo&i)al ti#es)ale 'hi)h stret)hes ro# the?re)a#$rian to the #ost re)ent enooi)(

R3$+

( ?lu##er an" D( M)=eary, 1997( Ph2!+& G**12( uy t

C( Mun)aster, 1995( N#+& Ph2!+ &$% F#$%&'$& P&!+(

144



basic concepts underlying the science of geology

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