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Relative Dating – Lab Which geologic event occurred first?? Which rock layer formed first? How do you know? Which rock layer formed first? How do you know?

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Presentation on theme: "Relative Dating – Lab Which geologic event occurred first?? Which rock layer formed first? How do you know? Which rock layer formed first? How do you know?"— Presentation transcript:

1 Relative Dating – Lab Which geologic event occurred first?? Which rock layer formed first? How do you know? Which rock layer formed first? How do you know? Geologic relative dating Lab

2 Relative Dating: Unraveling earth history by placing geologic events in chronological order Which geologic process came first? Relative Dating: Unraveling earth history by placing geologic events in chronological order Which geologic process came first? NO actual numbers applied!

3 Objectives: To observe exposures of rock and decipherTo observe exposures of rock and decipher the geologic history the geologic history Use relative dating principles to unravelUse relative dating principles to unravel geologic history geologic historyObjectives: To observe exposures of rock and decipherTo observe exposures of rock and decipher the geologic history the geologic history Use relative dating principles to unravelUse relative dating principles to unravel geologic history geologic history Which layer was deposited first A,B,C,D, or E?? Which layer was deposited first A,B,C,D, or E?? A B C D E Igneous dike

4 Lets unravel some geologic history from observations of various formations and their contacts Lets unravel some geologic history from observations of various formations and their contacts Nicholas Steno – 1669 proposed the following relative dating principles 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 The principle of Original Horizontality: Sedimentary rock layers are deposited as horizontal strata Any observed non-horizontal strata has been disturbed Sediment input A A B B C C

5 Strata has been deposited in horizontal layers Original Horizontality Strata has been deposited in horizontal layers Original Horizontality

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

7 Which strata are older and younger?? Oldest Youngest

8 The principle of Inclusions A piece of rock (clast) that has become includedA piece of rock (clast) that has become included in another rock body is older than the rock body in another rock body is older than the rock body it has become part of – why? it has become part of – why? The principle of Inclusions A piece of rock (clast) that has become includedA piece of rock (clast) that has become included in another rock body is older than the rock body in another rock body is older than the rock body it has become part of – why? it has become part of – why? Rock body A Intrusion of pluton B A A A A A A Older (rock A was there first)

9 Which granites are older and younger? OLDER YOUNGER

10 The principle of Cross Cutting relationships Any geologic feature that cuts across another geologicAny geologic feature that cuts across another geologic feature is younger feature is younger The principle of Cross Cutting relationships Any geologic feature that cuts across another geologicAny geologic feature that cuts across another geologic feature is younger feature is younger Is layer 5 older or younger than the intrusive dike ?? Is layer 5 older or younger than the intrusive dike ??

11 Which dikes formed first? A B C Qtz-Asp Vn

12 Given this sequence of rock layers, Whats wrong with the timing of events???? Given this sequence of rock layers, Whats wrong with the timing of events???? Oldest Youngest A time of erosion or non-deposition missing time A time of erosion or non-deposition missing time

13 The principle of Unconformities Rock surface that represents a period of erosion or non depositionRock surface that represents a period of erosion or non deposition Referred to missing timeReferred to missing time Three major types of unconformitiesThree major types of unconformities DisconformityDisconformity Angular unconformityAngular unconformity Non-conformityNon-conformity The principle of Unconformities Rock surface that represents a period of erosion or non depositionRock surface that represents a period of erosion or non deposition Referred to missing timeReferred to missing time Three major types of unconformitiesThree major types of unconformities DisconformityDisconformity Angular unconformityAngular unconformity Non-conformityNon-conformity Unconformity Disconformity uncon in non-disturbed sedimentary Disconformity – uncon in non-disturbed sedimentary layers layers Disconformity uncon in non-disturbed sedimentary Disconformity – uncon in non-disturbed sedimentary layers layers Angular uncon – uncon lies between angled strata and overlying horizontal strata and overlying horizontal strata Angular uncon – uncon lies between angled strata and overlying horizontal strata and overlying horizontal strata Non-conformity – sedimentary strata overlies crystalline overlies crystalline rocks (ig and met) rocks (ig and met) Non-conformity – sedimentary strata overlies crystalline overlies crystalline rocks (ig and met) rocks (ig and met)

14 Xln rocks Sedimentary rocks Disconformity Angular Unconformity Angular Unconformity Nonconformity

15 Lets apply the principles and unravel earths history Which came first? -- start with oldest to youngest Lets apply the principles and unravel earths history Which came first? -- start with oldest to youngest A B CD E F G H I Deposition of layers E,D,C,B,A E,D,C,B,A Tilting of layers E,D,C,B,A E,D,C,B,A Angular Uncon F Deposition of layers G,H,I G,H,I oldestoldest youngestyoungest

16 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. Understand the various types of rock (lithologic) symbols in conjunction to the principles to determine the geologic history of an area. deposition emplacement

17 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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