8 geologic time relative dating [uyumluluk...

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GEOLOGIC TIME

(Monroe&Wicander, 2005)Prof.Dr.Kadir Dirik Lecture Notes

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Geologic Time Table

R. Palmer, “The Decade of North American Geology, 1983Geologic Time Scale.” Geology (Geological Society of America, 1983), p. 504Prof.Dr.Kadir Dirik Lecture Notes

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Dating Methods in GeologyThere are two basic methods for dating in geology: (1) relative dating(göreceli yaşlandırma), and (2) absolute dating (mutlak yaşlandırma).Relative dating methodsThese methods allow events to be placed in sequential order and donot tell us how log ago an event took place.Fundamental principles of geology:(1) Principle of original horizantality (Orijinal yataylık prensibi),(2) Principle of superposition (Üst üste bulunma prensibi/süperpozisyonprensibi),(3) Principle of cross-cutting relationship (Birbirini kesme ilişkisi prensibi ),(4) Principle of inclusion (Kapanım/İnklüzyon prensibi),(5) Principle of lateral continuity (Yanal devamlılık prensibi),(6) Principle of fossil succession (Fosil dizileri).

Prof.Dr.Kadir Dirik Lecture Notes

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Principle of superposition (Üst üste bulunma prensibi)The Danish anatomist Nicolas Steno’s (1638-1686) observed that in anundisturbed succession of sedimentary rock layers, the oldest rock is atthe bottom and the youngest layer is at the top. This principles ofsuperposition is the basis for relative-age determination of strata andtheir contained fossils.

Principle of original horizantality (Orijinal yataylık prensibi)Steno also observed that, because sedimentary particles settle fromwater under the influence of gravity, sediments is deposited in essentiallyhorizontal layers, thus, illustrating the principles of originalhorizontality. Therefore, a sequence of sedimentary rock layers that issteeply inclined from the horizontal must have been tilted afterdeposition and lithification.


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(a) (b)

(c)Prof.Dr.Kadir Dirik Lecture Notes


Principle of lateral continuity (Yanal devamlılık prensibi)Steno’s third principle, the principle of lateral continuity, states that a layerof sediment extends laterally in all directions until it thins and pinch out orterminates against the age of the depositional basin.

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A dark dyke has been intruded into older light-colored granite.

James Hutton is credited with discovering the principles of cross-cutting relationships, He recognized that an ignous intrusion or faultmust be younger than the rocks it intrudes or displaces by fault.

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The principles of cross-cutting relationships (Kesişme ilişkisi)

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A fault (arrows shows direction of movement) displacing tilted beds, must be younger than the tilted beds.

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(a) A buried lava flow in bed 4 baked the underlying bed and bed 5contains inclusions of the lava flow. The lava flow is younger than bed 3and older than beds 5 and 6. (b) the rock units above and below the sill inbed 3 have been baked, indicating that the sill is younger than beds 2and 4.

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Principle of inclusionRelative ages of lava flow and sills

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(a)The batholith is younger than the sandstone because has been baked at its contact with the granite and the granite contains sandsone inclusions.

(b) Granite inclusion in sandsone indicate that the batholit was the source of sandstone and therefore is older.

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(Monroe&Wicander, 2005)

This principles states that, the fossils at the bottom of a sequence of strataare older than those at the top of the sequence. According to this principle,fossil assemblages succeed one another through time in a regular andpredictable order. The generelized diagram shows how geologists use theprinciples of fossil succession to identify strata of the same age in different areas.The rocks in the three sections encompassed by the dashed lines contain similarfossils and are thus the same age.


Principles of fossil succession or principles of faunal or floralsuccession


UNCONFORMITIESRepresenting times of nondeposition, erosion or both

ParaconformityDisconformityAngular unconformityNonconformity

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A simplified diagram showing the development of an unconformity and a hiatus. (a) Deposition began 12 million years ago (MYA) and continued more or less uninterrupted until 4 MYA. A 1-million-year episode of erosion occured, and during that time strata representing 2 million years of geologic time were eroded. (c) A hiatus of 3 billion years exists between the the older strata and the starata that formed during arenewed episode of deposition that began 3 MYA. (d) The actual stratigraphic record. The unconformity is the surface separating the strata and represents a major break in our record of geologic time.


Time of erosion

Amount of rock removed

by erosion

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DISCONFORMITY


Deposition

Uplift and erosion

Deposition

Disconcormity

Uplift

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ANGULAR UNCONFORMITY


Deposition

Uplift and tilting

Deposition

Uplift

Erosion

Angularunconformity

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NONCONFORMITY


Deposition

Intrusion of magna

Uplift

Uplift and erosion of overlying sediments

Nonconformity

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Deposition


Uplift, tilting, and faulting


Erosion


Deposition


Intrusion


Uplift and erosion


Deposition


Intrusion


Lava flow


Deposition

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