Stratigraphy Images

8/18/2019 Stratigraphy Images

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StratigraphyStratigraphy

StratigraphyStratigraphy:: study of the composition, geometry,study of the composition, geometry,

sequence, history and genesis of rocks andsequence, history and genesis of rocks andunconsolidated materials.unconsolidated materials.

Originally developed to bring order to layered rocksOriginally developed to bring order to layered rocks

(strata) and the events recorded therein, but(strata) and the events recorded therein, but

applicable to all Earth materials.applicable to all Earth materials.

Nicholas StenoNicholas Steno1638-1686

Born in Denmark, Settled in Italy

From observing the effects of floods,Steno concluded:

Particles settle from fluid in proportion to their sizeand cover the surface in an even layer.

Any change in particle size leads to development of horizontal layering = stratification

(layer=stratum, strata [plural])Solid rocks that he was seeing deposited from fluids.


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StenoSteno’’s Principless Principles

More principles for relative ageMore principles for relative age

Principle of inclusions

Principle of CrossCutting Relations


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NorthNorthAmericaAmerica

StratigraphicStratigraphic

CodeCode

(2005(2005

update)update)

Classes of Classes of stratigraphicstratigraphic unitsunitsI. Material categories based on content or physical limitsI. Material categories based on content or physical limits

LithostratigraphicLithostratigraphic:: sedimentary, extrusive igneous, ormetasedimentary or metavolcanic strata distinguished by lithiccharacteristics and stratigraphic position (conform to Law of Superposition).

LithodemicLithodemic:: chiefly intrusive igneous or highly deformed rock,extrusive igneous, or metasedimentary or metavolcanic stratadistinguished by lithic characteristics (generally don’t conformto Law of Superposition).

MagnetopolarityMagnetopolarity:: units unified by specific magnetic properties;

distinct from underlying and overlying magnetostratigraphicunits.

BiostratigraphicBiostratigraphic:: classification of bodies of rock based on theirfossil content.

AllostratigraphicAllostratigraphic:: mappable units of rock that are identified onthe basis of bounding discontinuities.

PedostratigraphicPedostratigraphic:: units consist of rock with one or morepedological horizons developed in one or morelithostratigraphic, lithodemic, or allostratigraphic unit.


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Classes of Classes of stratigraphicstratigraphic unitsunits

II. CategoriesII. Categories expressing or related to geologic ageexpressing or related to geologic age

A. Material categories used to define temporal spansA. Material categories used to define temporal spans

ChronostratigraphicChronostratigraphic:: a body of rock established to serve as the

material reference for all rocks formed during the same span of time. Each boundary is synchronous.

Polarity-chronostratigraphicPolarity-chronostratigraphic:: a body of rock that contains theprimary magnetic-polarity record imposed when the constituentrock was deposited or crystallized during a specific interval of geologic time.

B. Temporal (non-material) categoriesB. Temporal (non-material) categories

GeochronologicGeochronologic:: divisions of time distinguished on basis of therock record, as expressed by chronostratigraphic units. Not arock unit; it is a span of time.

Polarity-Chronologic:Polarity-Chronologic: divisions of time distinguished on basis of the record of magnetic-polarity, as expressed by polarity-

chronostratigraphic units.GeochronometricGeochronometric:: units established through direct division of

geologic time, expressed in years. Not based on time spansdesignated by the rock record.


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LithostratigraphicLithostratigraphic ClassificationClassification

! Article 24.—FormationFormation. The formation is the

fundamental unit in lithostratigraphicclassification. A formation is a body of rockidentified by lithic characteristics and

stratigraphic position; it is prevailingly but notnecessarily tabular and is mappable at theEarth’s surface or traceable in the subsurface.

LithostratigraphicLithostratigraphic ClassificationClassification

!! SupergroupSupergroup - assemblage of related or superposed

groups. Regional to provincial scale.

!! GroupGroup - express natural relations among formations.

Small-scale to regional scale.

!! FormationFormation - see prior page.

!! MemberMember - part of formation with distinguishing traits.

!! BedBed - smallest unit

•• Key or marker bedKey or marker bed - thin distinctive bed that is widelydistributed.

•• FlowFlow - smallest formal unit in extrusive volcanics.


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Unit definition - boundary typesUnit definition - boundary types

Often arbitrary boundaries if contact properties are gradational.Lithostratigraphic boundaries are rarely synchronous.

Unit definition - boundary typesUnit definition - boundary types


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LithodemicLithodemic ClassificationClassification

BiostratigraphicBiostratigraphic ClassificationClassification

Article 48.—Fundamentals ofFundamentals of biostratigrpahybiostratigrpahy.Biostratigraphy is the branch of stratigraphy thatdeals with the distribution of fossils in thestratigraphic record and the classification of bodiesof rock or rock material into biostratigraphic unitsbased on their contained fossils.

Remark. (a) Uniqueness.—Biostratigraphic unitsare distinct from all other kinds of stratigraphicunits because their contained fossils record theunidirectional process of organic evolution. Assuch, the stratigraphic record as a whole containsan unrepeated sequence of fossil taxa that may beused to determine the relative age of theirenclosing strata.


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George Cuvier (1769-1832)

French, Paleontologists/Geologist

William Smith (1769-1839)English, Geologist

(first geologic map)

Faunal successionFaunal succession

Types ofTypes of biozonesbiozones1.Range biozone (A,B)2.Interval biozone (C,D)

3.Lineage biozone (E)4.Assemblage biozone (F)

5.Abundance biozone (G)

F. G.


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PedostratigraphicPedostratigraphic classificationclassification

Based on fossil soils.

AllostratigraphicAllostratigraphic classificationclassificationBased on discontinuities


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Geologic Time ScaleGeologic Time Scale

!! EonEon

•• EraEra

!! PeriodPeriod

•• EpochEpoch

!! AgeAge

!! EonothemEonothem

•• ErathemErathem

!! SystemSystem

•• SeriesSeries

!! StageStage

GeochronologicGeochronologic

(Time)(Time)ChronostratigraphicChronostratigraphic

(Rock)(Rock)


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Time ScaleTime Scale

For example:For example: MaastrichtianMaastrichtian AgeAge

!! PhanerozoicPhanerozoic EonEon•• Mesozoic EraMesozoic Era

!! Cretaceous PeriodCretaceous Period•• Late Cretaceous EpochLate Cretaceous Epoch

!! MaastrichtianMaastrichtian AgeAge

!! Start defined by: Mean of 12Start defined by: Mean of 12 biostratigraphicbiostratigraphic criteria of criteria of equal importance. Closely above is lowest occurrence of equal importance. Closely above is lowest occurrence of ammoniteammonite Pachydiscus neubergicusPachydiscus neubergicus. Boreal proxy is lowest. Boreal proxy is lowestoccurrence of belemniteoccurrence of belemnite Belemnella lanceolataBelemnella lanceolata..

•• 70.6 ± 0.6 Ma70.6 ± 0.6 Ma

!! End Defined By: Iridium Anomaly. Associated with a majorEnd Defined By: Iridium Anomaly. Associated with a majorextinction horizon (foraminifers, calcareousextinction horizon (foraminifers, calcareous nannofossilsnannofossils,,dinosaurs, etc.)dinosaurs, etc.)

•• 65.5 ± 0.3 Ma65.5 ± 0.3 Ma

Time ScaleTime Scale

!! For example:For example: LutetianLutetian AgeAge

!! PhanerozoicPhanerozoic EonEon•• Cenozoic EraCenozoic Era

!! PaleogenePaleogene PeriodPeriod•• Eocene Epoch (Sub-epoch: Middle Eocene)Eocene Epoch (Sub-epoch: Middle Eocene)

!! LutetianLutetian AgeAge

!! Start Defined By:Start Defined By: PlanktonicPlanktonic foraminifer, lowestforaminifer, lowest

occurrence ofoccurrence of HantkeninaHantkenina..•• 48.6 ± 0.2 Ma48.6 ± 0.2 Ma

!! End Defined By: Near extinction of calcareousEnd Defined By: Near extinction of calcareousnannofossilnannofossil Reticulofenestra reticulataReticulofenestra reticulata..•• 40.4 ± 0.2 Ma40.4 ± 0.2 Ma


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StratigraphicStratigraphic CorrelationCorrelation

How do we put stratigraphic

columns that are separatedin space into relativetemporal order?

!! LithostratigraphicLithostratigraphic

!! BiostratigraphicBiostratigraphic

!! MagnetostratigraphicMagnetostratigraphic

!! GeochronologicGeochronologic

!! ChemostratigraphicChemostratigraphic (e.g. iridium(e.g. iridium

anomaly at K-T boundary)anomaly at K-T boundary)

StratigraphicStratigraphic CorrelationCorrelation


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Top of Navajo

Top of Kaibab

LithostratigraphicLithostratigraphic

CorrelationCorrelation

Based on lateralcontinuity.


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Rock Description and CreationRock Description and Creation

of aof a LithostratigrpahicLithostratigrpahic ColumnColumn


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Encountering a SedimentaryEncountering a Sedimentary

SectionSection

!! Attributes of particlesAttributes of particles

•• Grain-sizeGrain-size

•• Sorting (poorly toSorting (poorly to well sorted)well sorted)

•• Rounding (angular to rounded)Rounding (angular to rounded)

•• Particle and matrix/cement compositionParticle and matrix/cement composition

!! Contacts between bedsContacts between beds

!! Sedimentary StructuresSedimentary Structures

!! Fossils,Fossils, BioturbationBioturbation

ContactsContacts!! Primary StructuresPrimary Structures

•• StratigraphicStratigraphic contactscontacts

•• YoungingYounging DirectionDirection

•• UnconformitiesUnconformities

!! Intrusive contactsIntrusive contacts•• Sills and dikesSills and dikes

•• BatholithsBatholiths

!! Fault ContactsFault Contacts•• Normal, thrust, strike-slipNormal, thrust, strike-slip

!! FoldsFolds•• Anticlines, synclines Anticlines, synclines


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Is the sedimentary successionIs the sedimentary succession

right-side up?right-side up?

Primary StructuresPrimary Structures

Pillow BasaltsPillow Basalts


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Sedimentary StructuresSedimentary Structures

StromatolitesStromatolites, Belt, Belt GpGp., MT., MT

Graded bedsGraded beds


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Sedimentary StructuresSedimentary Structures

AncientAncient MudcracksMudcracks

Basic Question:Basic Question:Is the section conformable?Is the section conformable?

!! Is the sedimentary pileIs the sedimentary pile

continuous?continuous?


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UnconformitiesUnconformities

DisconformityDisconformity: same beddingattitude above and below with missingtime (depositional hiatus)

Angular UnconformityAngular Unconformity: upper bedstruncate lower deformed strata

NonconformityNonconformity: Sedimentary rocksabove low-relief erosional surface incrystalline rocks

Buttress UnconformityButtress Unconformity:Sedimentary strata onlap onto high-relief erosional surface

DisconformityDisconformity

Maybe difficult to recognize with out a dramatic change in rock type or abreak in stratigraphic ages for a well dated succession


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Nonconformity: Grand CanyonNonconformity: Grand Canyon

Angular Unconformity: Grand CanyonAngular Unconformity: Grand Canyon

Cambrian Tapeats Sandstone (550 Ma) over tilted Grand CanyonSupergroup (1.2-0.8 Ga) rocks


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Angular unconformityAngular unconformity

Death ValleyDeath Valley

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