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Geologic relative dating Lab. Which rock layer formed first? How do you know?. Relative Dating – Lab Which geologic event occurred first??. Relative Dating : Unraveling earth history by placing geologic events in chronological order “Which geologic process came first”?.

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Geologic relative dating Lab

Which rock layer formed first?

How do you know?

Relative Dating – Lab

Which geologic event occurred first??


Relative Dating:

Unraveling earth history by

placing geologic events in

chronological order

“Which geologic process came first”?

NO actual numbers applied!


  • the geologic history

    • Use relative dating principles to unravel

    • geologic history

  • D

    C

    B

    E

    A

    Igneous dike

    Which layer was deposited first

    A,B,C,D, or E??


    Let’s unravel some geologic history from observations of

    various formations and their contacts

    Nicholas Steno – 1669 proposed the following relative

    dating principles

    • The principle of Original Horizontality:

      • Sedimentary rock layers are deposited as horizontal strata

      • Any observed non-horizontal strata has been disturbed

    Sediment input

    C

    B

    A



    • The principle of Superposition

      • In any undisturbed sequence of strata, the oldest stratum is at the bottom of the sequence and the youngest stratum is on top.

    5

    Youngest

    4

    3

    2

    1

    Oldest


    Which strata are older and younger??

    Youngest

    Oldest


    • The principle of Inclusions

      • A piece of rock (clast) that has become “included”

      • in another rock body is older than the rock body

      • it has become part of – why?

    Rock body A

    A

    A

    A

    Older (rock A was there first)

    Intrusion of pluton B


    Which “granites” are older and younger?

    OLDER

    YOUNGER


    • The principle of Cross Cutting relationships

      • Any geologic feature that cuts across another geologic

      • feature is younger

    5

    Is layer 5 older

    or younger than

    the intrusive

    dike ??

    4

    3

    2

    6

    1


    A

    B

    C

    Qtz-Asp Vn

    Which dikes formed first?


    Given this sequence of rock layers, “What’s

    wrong with the timing of events????

    A time of erosion

    or non-deposition

    “missing time”

    Youngest

    7

    6

    3

    2

    1

    Oldest


    • The principle of Unconformities

      • Rock surface that represents a period of erosion or non deposition

      • Referred to “missing time”

      • Three major types of unconformities

        • Disconformity

        • Angular unconformity

        • Non-conformity

    Disconformity – uncon in non-disturbed sedimentary

    layers

    Angular uncon – uncon lies between angled strata

    and overlying horizontal strata

    Non-conformity – sedimentary strata

    overlies crystalline

    rocks (ig and met)

    Unconformity


    Disconformity

    Angular

    Unconformity

    Sedimentary rocks

    Nonconformity

    Xln rocks


    Let’s apply the principles and unravel earth’s history

    Which came first? -- start with oldest to youngest

    I

    Deposition of layers

    G,H,I

    youngest

    H

    G

    Angular Uncon F

    A

    F

    Tilting of layers

    E,D,C,B,A

    B

    C

    D

    E

    Deposition of layers

    E,D,C,B,A

    oldest


    Rock symbols (rock legends)

    Understand the various types

    of rock (lithologic) symbols in

    conjunction to the principles to

    determine the geologic history

    of an area.

    emplacement

    deposition


    The principle of Faunal (fossil) succession

    This principle is attributed to William Smith, an English engineer in the late 1700s. Smith noticed that the kinds of fossils he found changed through a vertical succession of rock layers, and furthermore, that the same vertical changes in fossils occurred in different places.


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